The genome of Caenorhabditis elegans contains representatives of the channel families found in both vertebrate and invertebrate nervous systems. However, it lacks the ubiquitous Hodgkin-Huxley Na+ channel that is integral to long-distance signaling in other animals. Nematode neurons are presumed to communicate by electrotonic conduction and graded depolarizations. This fundamental difference in operating principle may require different channel populations to regulate transmission and transmitter release. We have sampled ionic channels from the somata of two chemosensory neurons (AWA and AWC) of C. elegans. A Ca2+-activated, outwardly rectifying channel has a conductance of 67 pS and a reversal potential indicating selectivity for K+. An inwardly rectifying channel is active at potentials more negative than -50 mV. The inward channel is notably flickery even in the absence of divalent cations; this prevented determination of its conductance and reversal potential. Both of these channels were inactive over a range of membrane potentials near the likely cell resting potential; this would account for the region of very high membrane resistance observed in whole-cell recordings. A very-large-conductance (> 100 pS), inwardly rectifying channel may account for channel-like fluctuations seen in whole-cell recordings.