otal(ota = olfactory trap abnormal), an X-linked mutation ofDrosophilaisolated by virtue of abnormal olfactory behavior, is shown to be an allele ofrdgB(retinal degeneration B), a gene required for normal visual system physiology.rdgBfunction is shown to be necessary for olfactory response of both adult flies and larvae, which have distinct olfactory systems. Electrophysiological recordings from the adult antenna indicate thatrdgBis required for normal response in the peripheral olfactory system: somerdgBmutants show a delayed return to the resting potential following stimulation with ethyl acetate vapor. These results indicate thatrdgBis required for both visual and olfactory physiology, and they suggest that visual and olfactory transduction may share at least one common molecular step inDrosophila.