Retinitis pigmentosa (RP) constitutes a group of genetically heterogeneous progressive photore-ceptor degenerations leading to blindness and affecting 50,000–100,000 people in the U.S. alone. Over 20 different RP loci have been mapped1, of which six have been identified. Three of these encode members of the rod photoreceptor visual transduction cascade2: rhodopsin3, the rod cGMP-gated cation channel α subunit4, and the β subunit of cGMP-phosphodiesterase (PDEB)5. As null mutations in PDEB cause some cases of RP and since both α and β subunits are required for full phosphodiesterase activity, we examined the gene encoding the α subunit of cGMP phosphodiesterase (PDEA) in 340 unrelated patients with RP. We found three point mutations in PDEA in affected members of two pedigrees with recessive RP. Each mutation alters an essential functional domain of the encoded protein and likely disrupts its catalytic function. PDEA is the seventh RP gene identified, highlighting the extensive genetic heterogeneity of the disorder and encouraging further investigation into the role of other members of the phototransduction cascade in RP. © 1995 Nature Publishing Group.