Spatial distribution of the cAMP-gated channel was investigated in amphibian olfactory receptor cells. Low doses of cAMP applied to the cytoplasmic side of a membrane patch excised from cilia produced single channel activity of unitary conductance 28pS. Variance analysis showed that the ciliary membrane contained 920 cAMP gated-channels/microns2 in the newt and 2400 channels/microns2 in the toad. In contrast, the membrane of the dendrite and cell body contained only 2 cAMP-gated channels/microns2 (newt) and 6 channels/microns2 (toad). Thus, there is a high density of cAMP-gated channels in the cilia where olfactory transduction is thought to take place.