Application of desglycine-arginine-vasopressin to spontaneously nonactive command neurones of the snail's defensive reflex in the process of low-frequency (2-4 min intervals) intracellular stimulation led under certain conditions to an increase of excitability that was expressed in the shortening of latency of action potential generation, increase of the number of action potentials in response to a stimulus of fixed value, increase of membrane resistance, lowering of critical level of membrane depolarization and amplifying of pacemaker activity. However in spite of unidirectional changes of all the recorded parameters, the increases of values, opposite to the latency, did not correlate with the increases of membrane resistance and correlated well with the changes of depolarization critical level. If desglycine arginine-vasopressin was added to the medium during worsening of the neurones' excitability was probably caused by the influence of desglycine-arginine-vasopressin on the membrane active properties.