We have isolated and characterized a new guanylyl cyclase gene (dgc1) in Drosophila. The deduced amino acid sequence (683 amino acids) most closely resembled the mammalian soluble-type guanylyl cyclase alpha subunit. The cyclase catalytic domain was highly conserved between the mammalian and Drosophila guanylyl cyclases. The dgc1 mRNA was detected in wild-type heads but not in bodies, and its level was reduced in the mutant eyes absent (eya), indicating that dgc1 is preferentially expressed in the CNS and in the eye. The enriched distribution in the eye suggests that dgc1 may have a role in phototransduction.