The effects of methohexital, succinylcholine, and electroconvulsive shock (ECS) on the estrous cycle were investigated. Eighty-eight rats, chosen on the basis of estrous stability, were selected from a subject pool of 106 animals and were randomly assigned to one of eight treatment conditions, with the restriction that each condition contain 11 animals. Treatments were as follows: one ECS, five ECSs, one ECS with methohexital and succinylcholine, five ECSs with methohexital and succinylcholine, one sham ECS (SECS), five SECSs, one SECS with methohexital and succinylcholine, and five SECSs with methohexital and succinylcholine. Consistent with preVIous reports, the five-, but not the one-, :BeS treatment produced a significant delay in estrus. However, the data indicated that when five ECS treatments were given to rats that had received methohexital and succinylcholine, no significant delay in estrus was observed. No estrous delays were observed following any of the remaining treatments, nor were additional delays observed after cycling began in the five-ECS treatment conditions.