Short-term heterosynaptic potentiation of cholinergic excitatory postsynaptic currents and potentials in defensive behavior command neurons was found to be evoked by stimulation of the visceral sac in the common snail. It is suggested that a mechanism increasing the choline resistance of the postsynaptic zones of command neuron membranes is involved in potentiating the excitatory postsynaptic responses to sensory stimulation.