In a first series of experiments, different selective dopamine D2 receptor agonists (B-HT 920, B-HT 958, SND 919, CQ 32-084, CQP 201-403, and lisuride) and the D1/D2 agonist apomorphine were IP injected into adult male rats. At low doses, they elicited repeated episodes of penile erection and stretching-yawning: at all doses tested, B-HT 920, B-HT 958, and CQ 32-084 also induced hypomotility, a sign that, in the case of high doses of SND 919, CQP 201-403, lisuride, and apomorphine, was replaced by stereotyped behaviour. In a second series of experiments, the same D2 agonists and the mixed D1/D2 agonist apomorphine were IP injected at the same doses into chicks. The following behavioural signs were observed: hypomotility, sleep-like state, and stereotyped pecking. The results show that: 1. there are similarities between the behavioural effects induced by the DA agonists in rats and chicks; and 2. in both species some behavioural signs elicited by the DA ergic compounds are useful pointers to their specific neurochemical activity.