We have determined the map position of the gene encoding a common precursor protein for diapause hormone and pheromone biosynthesis-activating neuropeptide (the DH-PBAN gene, Dh)in the silkmoth, Bombyx mori. First we compared the structure of introns in the DH-PBAN gene by the polymerase chain reaction, and found that the Dh locus carried three alleles, DhA1, DhA2 and DhB. The DhA1 and DhA2 alleles contained a fourth intron consisting of 740 bp, whereas DhB had a longer fourth intron of 770 bp. DhA1 and DhA2 contained a fifth intron consisting of 940 bp, whereas the fifth intron in DhB was much longer and consisted of 1700 bp. DhA1 was distinguished from DhA2 by an RFLP in the fifth intron after digestion with Rsa I. Linkage analyses using these polymorphisms showed that Dh was linked to the bp gene on chromosome 11, and independent of markers on chromosomes 1, 2, 3, 4, 5, 6, 7 and 13. To determine the map position, we obtained F1 hybrids between the n501 strain (K DhA1) and the w30 strain ( + KDhB), and backcrossed the F1 hybrid to females of the w30 strain. From the segregation of K and Dh in 864 individuals in the next generation, the recombination value was calculated as 25·5 % between K and Dh. Similarly we obtained backcross progeny between the No. 744 strain (BuDhA1) and the w30 strain ( + BuDhB), and calculated the recombination value between Bu and Dh as 30·4% from 487 progeny. Because k and Bu had already been mapped at positions 11–23·2 cM and 11–28·7 cM, respectively, we mapped Dh at 11--2·2 cM. The Dh locus is different from any loci which are known to control diapause, development or growth.