Untrained Pleurobranchaea feed voraciously when presented food and withdraw from electrical shocks. We trained experimental animals in ten trials spaced 1 hour apart to withdraw from food alone by electrically shocking them if they fed or were indifferent to food. The greatest increase in the number of learned withdrawal responses occurred within 12 hours after conditioning, and was accompanied by long-lasting increases in the threshold and latency of feeding responses. Control animals, which received food and shock alternately (unpaired) every half hour, showed considerably weaker changes than experimentals. These control responses quickly returned to initial levels after conditioning.