diff --git a/bwamem.c b/bwamem.c
index ae1ce68..5ee153a 100644
--- a/bwamem.c
+++ b/bwamem.c
@@ -69,7 +69,7 @@ mem_opt_t *mem_opt_init()
 	o->n_threads = 1;
 	o->max_matesw = 100;
 	o->mask_level_redun = 0.95;
-	o->min_HSP_score = 0;
+	o->min_chain_weight = 0;
 	o->mapQ_coef_len = 50; o->mapQ_coef_fac = log(o->mapQ_coef_len);
 //	o->mapQ_coef_len = o->mapQ_coef_fac = 0;
 	bwa_fill_scmat(o->a, o->b, o->mat);
@@ -357,6 +357,15 @@ int mem_chain_flt(const mem_opt_t *opt, int n_chn, mem_chain_t *chains)
 	flt_aux_t *a;
 	int i, j, n;
 	if (n_chn <= 1) return n_chn; // no need to filter
+	for (i = j = 0; i < n_chn; ++i) {
+		mem_chain_t *c = &chains[i];
+		int w;
+		w = mem_chain_weight(c);
+		if (w >= opt->min_chain_weight)
+			chains[j++] = *c;
+	}
+	n_chn = j;
+	if (n_chn == 0) return 0;
 	a = malloc(sizeof(flt_aux_t) * n_chn);
 	for (i = 0; i < n_chn; ++i) {
 		mem_chain_t *c = &chains[i];
@@ -526,10 +535,13 @@ void mem_mark_primary_se(const mem_opt_t *opt, int n, mem_alnreg_t *a, int64_t i
 
 #define MEM_SHORT_EXT 50
 #define MEM_SHORT_LEN 200
+
+#define MEM_HSP_COEF 1.5
+
 #define MAX_BAND_TRY  2
 
 /* mem_test_chain_sw() uses SSE2-SW to align a short chain with 50bp added to
- * each end of the chain. If the SW score is below opt->min_HSP_score, it will
+ * each end of the chain. If the SW score is below min_HSP_score, it will
  * return 0, informing the caller to discard the chain. This heuristic is
  * somewhat similar to BLAST which drops a seed hit if ungapped extension is
  * below a certain score (true for old BLAST; don't know how BLAST+ works).
@@ -547,6 +559,7 @@ void mem_mark_primary_se(const mem_opt_t *opt, int n, mem_alnreg_t *a, int64_t i
 int mem_test_chain_sw(const mem_opt_t *opt, int64_t l_pac, const uint8_t *pac, int l_query, const uint8_t *query, const mem_chain_t *c)
 {
 	int i, qb, qe;
+	int min_HSP_score = (int)(opt->min_chain_weight * opt->a * MEM_HSP_COEF + .499);
 	int64_t rb, re, rlen;
 	uint8_t *rseq = 0;
 	kswr_t x;
@@ -579,7 +592,7 @@ int mem_test_chain_sw(const mem_opt_t *opt, int64_t l_pac, const uint8_t *pac, i
 	assert(rlen == re - rb);
 	x = ksw_align2(qe - qb, (uint8_t*)query + qb, re - rb, rseq, 5, opt->mat, opt->o_del, opt->e_del, opt->o_ins, opt->e_ins, KSW_XSTART, 0);
 	free(rseq);
-	if (x.score >= opt->min_HSP_score) return 1;
+	if (x.score >= min_HSP_score) return 1;
 	if (bwa_verbose >= 4) printf("** give up the chain due to small HSP score %d.\n", x.score);
 	return 0;
 }
@@ -1014,7 +1027,7 @@ mem_alnreg_v mem_align1_core(const mem_opt_t *opt, const bwt_t *bwt, const bntse
 		mem_chain_t *p = &chn.a[i];
 		int ret;
 		if (bwa_verbose >= 4) err_printf("* ---> Processing chain(%d) <---\n", i);
-		if (opt->min_HSP_score > 0) ret = mem_test_chain_sw(opt, bns->l_pac, pac, l_seq, (uint8_t*)seq, p);
+		if (opt->min_chain_weight > 0) ret = mem_test_chain_sw(opt, bns->l_pac, pac, l_seq, (uint8_t*)seq, p);
 		else ret = mem_chain2aln_short(opt, bns->l_pac, pac, l_seq, (uint8_t*)seq, p, &regs);
 		if (ret > 0) mem_chain2aln(opt, bns->l_pac, pac, l_seq, (uint8_t*)seq, p, &regs);
 		free(chn.a[i].seeds);
diff --git a/bwamem.h b/bwamem.h
index dd68d16..27514cd 100644
--- a/bwamem.h
+++ b/bwamem.h
@@ -30,13 +30,13 @@ typedef struct {
 	int T;                  // output score threshold; only affecting output
 	int flag;               // see MEM_F_* macros
 	int min_seed_len;       // minimum seed length
+	int min_chain_weight;
 	float split_factor;     // split into a seed if MEM is longer than min_seed_len*split_factor
 	int split_width;        // split into a seed if its occurence is smaller than this value
 	int max_occ;            // skip a seed if its occurence is larger than this value
 	int max_chain_gap;      // do not chain seed if it is max_chain_gap-bp away from the closest seed
 	int n_threads;          // number of threads
 	int chunk_size;         // process chunk_size-bp sequences in a batch
-	int min_HSP_score;      // used in mem_test_chain(); disabled by default
 	float mask_level;       // regard a hit as redundant if the overlap with another better hit is over mask_level times the min length of the two hits
 	float chain_drop_ratio; // drop a chain if its seed coverage is below chain_drop_ratio times the seed coverage of a better chain overlapping with the small chain
 	float mask_level_redun;
diff --git a/fastmap.c b/fastmap.c
index 1db00cb..c971f9b 100644
--- a/fastmap.c
+++ b/fastmap.c
@@ -37,7 +37,7 @@ int main_mem(int argc, char *argv[])
 	opt = mem_opt_init();
 	opt0.a = opt0.b = opt0.o_del = opt0.e_del = opt0.o_ins = opt0.e_ins = opt0.pen_unpaired = -1;
 	opt0.pen_clip5 = opt0.pen_clip3 = opt0.zdrop = opt0.T = -1;
-	while ((c = getopt(argc, argv, "epaMCSPHk:c:v:s:r:t:R:A:B:O:E:U:w:L:d:T:Q:D:m:I:N:u:")) >= 0) {
+	while ((c = getopt(argc, argv, "epaMCSPHk:c:v:s:r:t:R:A:B:O:E:U:w:L:d:T:Q:D:m:I:N:W:")) >= 0) {
 		if (c == 'k') opt->min_seed_len = atoi(optarg);
 		else if (c == 'w') opt->w = atoi(optarg);
 		else if (c == 'A') opt->a = atoi(optarg), opt0.a = 1;
@@ -56,10 +56,10 @@ int main_mem(int argc, char *argv[])
 		else if (c == 'v') bwa_verbose = atoi(optarg);
 		else if (c == 'r') opt->split_factor = atof(optarg);
 		else if (c == 'D') opt->chain_drop_ratio = atof(optarg);
-		else if (c == 'u') opt->min_HSP_score = atoi(optarg);
 		else if (c == 'm') opt->max_matesw = atoi(optarg);
 		else if (c == 's') opt->split_width = atoi(optarg);
 		else if (c == 'N') opt->max_chain_gap = atoi(optarg);
+		else if (c == 'W') opt->min_chain_weight = atoi(optarg);
 		else if (c == 'C') copy_comment = 1;
 		else if (c == 'Q') {
 			opt->mapQ_coef_len = atoi(optarg);
@@ -102,7 +102,7 @@ int main_mem(int argc, char *argv[])
 		else return 1;
 	}
 	if (opt->n_threads < 1) opt->n_threads = 1;
-	if (opt->T < opt->min_HSP_score) opt->T = opt->min_HSP_score;
+//	if (opt->T < opt->min_HSP_score) opt->T = opt->min_HSP_score; // TODO: tie ->T to MEM_HSP_COEF
 	if (optind + 1 >= argc || optind + 3 < argc) {
 		fprintf(stderr, "\n");
 		fprintf(stderr, "Usage: bwa mem [options] <idxbase> <in1.fq> [in2.fq]\n\n");
@@ -125,7 +125,6 @@ int main_mem(int argc, char *argv[])
 		fprintf(stderr, "       -E INT[,INT]  gap extension penalty; a gap of size k cost '{-O} + {-E}*k' [%d,%d]\n", opt->e_del, opt->e_ins);
 		fprintf(stderr, "       -L INT[,INT]  penalty for 5'- and 3'-end clipping [%d,%d]\n", opt->pen_clip5, opt->pen_clip3);
 		fprintf(stderr, "       -U INT        penalty for an unpaired read pair [%d]\n", opt->pen_unpaired);
-		fprintf(stderr, "       -u INT        drop a chain if local SW score below INT; 0 to disable [%d]\n", opt->min_HSP_score);
 		fprintf(stderr, "\nInput/output options:\n\n");
 		fprintf(stderr, "       -p            first query file consists of interleaved paired-end sequences\n");
 		fprintf(stderr, "       -R STR        read group header line such as '@RG\\tID:foo\\tSM:bar' [null]\n");
@@ -141,7 +140,7 @@ int main_mem(int argc, char *argv[])
 		fprintf(stderr, "                     FR orientation only. [inferred]\n");
 		fprintf(stderr, "\n");
 		fprintf(stderr, "Note: Please read the man page for detailed description of the command line and options.\n");
-		fprintf(stderr, "      `-k18 -u200 -w200 -c1000 -r10 -A3 -O3 -E1' is recommended for PacBio reads as of early 2014.\n");
+		fprintf(stderr, "      `-k17 -W40 -w200 -c1000 -r10 -A2 -O2 -E1' is recommended for PacBio reads as of early 2014.\n");
 		fprintf(stderr, "\n");
 		free(opt);
 		return 1;
diff --git a/main.c b/main.c
index 9dc0cdf..1089477 100644
--- a/main.c
+++ b/main.c
@@ -4,7 +4,7 @@
 #include "utils.h"
 
 #ifndef PACKAGE_VERSION
-#define PACKAGE_VERSION "0.7.8+dev-r461"
+#define PACKAGE_VERSION "0.7.8+dev-r462"
 #endif
 
 int bwa_fa2pac(int argc, char *argv[]);