Experiments were performed to study the individual and combined effects of amphetamine and imipramine in rats with lowered brain catecholamines or 5-HT levels. The stereotyped behaviour was studied employing the Open Field test apparatus. When the brain catecholamine level was lowered by -methyl tyrosine, amphetamine failed to induce complex stereotyped behaviour, while disulfiram pretreatment did not significantly alter the complex stereotyped behaviour due to amphetamine. However, pretreatment with either -methyltyrosine or p-chlorophenylalanine modified the effects of imipramine. Imipramine augmented the amphetamine induced stereotype behaviour. Pretreatment with -methyl tyrosine, p-chlorophenylalanine or disulfiram altered the behavioural effects due to the interaction of imipramine and amphetamine. These findings suggest that catecholamines, particularly brain dopamine, play a greater role in the stereotype behaviour due to amphetamine and its augmentation by imipramine.