A group of rats was treated with a double electroconvulsive shock (ECS) applied contingently after conditioning sessions on a continuous reinforcement (CRF) schedule. The rats were allowed to make 20 responses per session. Another group of subjects not treated with ECS was used as a control group. Later, two long CRF sessions without treatment were given to equate the experimental and control groups. Following this training, all animals received three extinction sessions. The two first sessions were followed by a double ECS for half of the subjects in each group (control and experimental). Different rates of conditioning and extinction were studied. In acquisition, an ECS effect was observed which increased with successive treatment and had an opposite trend to the practice effect. In extinction, ECS did not have a significant effect, although a similar trend was observed. © 1979, Psychonomic Society, Inc.. All rights reserved.