In a situation of associative learning a phenomenon of conditioned inhibition of action potential (AP) generation was found in large isolated identified neurons of Helix pomatia, including LPa3 and RPa3. It is formed by the use of two above-threshold electrical stimuli, inducing stable spike generation. The effective time interval between the two above-threshold electrical stimuli ranged from 5 to 2500 msec. Conditioned inhibition of AP generation after the first two series of trainings lasted 10-15 min. The use of a test stimulus showed that conditioned inhibition is characterized by selectivity, localization, and specificity. Pseudolearning controls showed that conditioned inhibition of AP generation satisfies the demand, and it is consequently one form of conditioned response occurring in a completely isolated neuron.