The effects of CGRP antiserum on passive avoidance behaviour were tested in rats. Intracerebroventricular (i.c.v.) administration of CGRP antiserum immediately after a single learning trial attenuated the passive avoidance responses when the animals were tested for 24 h retention. Significant decreases in avoidance latency were found at CGRP antiserum dilutions of 1:20 and 1:40. The data supported the assumption that endogenous brain CGRP may be a modulator in learning-associated memory processes.