Behavioural effects of somatostatin after intracerebroventricular (icv) administration have been investigated in male rats. In a passive avoidance learning test, somatostatin (1 microgram), given 30 min before the learning session, increased the avoidance latency at 24 h, but not at 48 h, after the injection, when compared to a 10 micrograms treated group. However, compared to a saline treated group, somatostatin (0.01, 0.1, 1, or 10 micrograms) did not significantly influence the avoidance latency. In a shuttle box experiment somatostatin (1 microgram) facilitated the learning process. In an open-field behaviour test, immediately after the 24 h passive avoidance test, 10 micrograms of the peptide decreased the rearing activity without influencing other open field behaviours, like locomotion, grooming and defecation. In a second open-field experiment somatostatin (1 microgram), given 30 min prior to the test, similarly as in the shuttle box learning experiment, increased the locomotion of the animals. These data suggest that somatostatin influences both the passive avoidance and shuttle box behaviours. The peptide-induced motor performance of the animals may play an important role in influencing the responses observed in these behavioural tests.