Cyclic nucleotide gated (CNG) cation channels are critical for signal transduction in vertebrate visual and olfactory systems. Members of the CNG channel gene family have now been cloned from a number of species, from Caenorhabditis elegans to humans. An important advance has been the discovery that CNG channels are present in many neurons of the mammalian brain. CNG channels act as molecular links between G-protein-coupled cascades, Ca2+-signalling systems, and gaseous messenger pathways. Perhaps most striking are recent data implicating CNG channels in both developmental and synaptic plasticity.