Five hundred and thirty-two nanometers laser light evokes neuron-specific electrical responses in identified neurons of Helix ganglia. Such responses are intensity-dependent over the range 25-1500 mW, readily reversible and repeatable. Detailed experiments on the C1 neuron, which is inhibited by 532nm light, showed that inhibition results from a selective increase in transmembrane Cl- ion conductance. Experiments with calcium-sensitive microelectrodes suggest that the response does not result from an increase in I Ca2+](i). The change in Cl- ion conductance probably occurs in the extensive plasmalemma infoldings of the proximal axon. (C) 2008 Elsevier Ireland Ltd. All rights reserved.