Cyclic nucleotides are important second messengers that mediate a number of cellular responses to external signals. Cyclic nucleotide phosphodiesterases play a role in signal transduction by regulating the cellular concentrations of these messengers. Here, we have applied Southern analyses of somatic cell hybrid lines and of recombinant inbred (RI) mouse strains as well as fluorescence chromosomal in situ hybridization (FISH) to chromosomally localize five cAMP-specific nucleotide phosphodiesterase genes in human and mouse. Genes DPDE1, DPDE2, DPDE3, and DPDE4 that share sequence homology with the Drosophila dunce gene were assigned to human chromosome 19 (DPDE1 and DPDE2), 5q12 (DPDE3), and 1p31 (DPDE4) and to mouse chromosomes 8, 9, 13, and 4, respectively. The high-affinity cAMP-specific phosphodiesterase gene (HCP1) was mapped to human chromosome 8q13-q22. Since these genes are potential candidates for involvement in psychiatric or behavioral disorders, knowledge of their chromosomal localizations will facilitate the discovery of their association with disease genes as they are being mapped by linkage studies.