Administration to mice of electroconvulsive shock (ECS) five times over 10 days results in an enhanced 5-HTP-induced head twitch response, an enhanced apomorphine-induced locomotor response and an attenuated sedation response to the alpha 2-adrenoceptor agonist clonidine. Diazepam (1.25 mg/kg IP) injected 5 min before each ECS abolished the enhanced 5-HT- and dopamine-mediated responses but left the attenuated sedation response unaltered. When diazepam was given 5 min after each convulsion it still had the same effect, although its effects on the ECS-induced changes was blocked by administration of the specific benzodiazepine antagonist Ro 15-1788 (10 mg/kg IP) at the same time as diazepam. It is concluded that diazepam can abolish the ECS-induced changes in 5-HT- and DA-mediated behaviour, but not alpha 2-adrenoceptor-mediated responses, possibly by interfering with post-ictal changes. The implications for administration of benzodiazepines during electroconvulsive therapy (ECT) are discussed.