Pairs of neonate chicks were administered psychoactive agents and pecks against each other were recorded during 4-hr test sessions. The first experiment assessed where drug-induced aggressive pecking could serve as a useful anti-depressant screening model. Although pecking was induced by tricyclics, d-amphetamine, and L-Dopa, ineffective agents included a MAO inhibitor (pargline) and a tricyclic indole antidepressant (iprindole). These data cast doubt on the validity of the chick pecking model as a specific antidepressant tests. A second experiment attempted to determine where different amines were involved in pecking induced by an antidepressant and a CNS stimulant. Pairs of chicks were pretreated with various doses of amine antagonists, and a standard dose of imipramine (IMI) or d-amphetamine (AMP) was administered. Haloperidol completely antagonized AMP but not IMI pecking, while phentolamine and propranolol did not modify AMP pecking, suggesting involvement of dopamine. Pecking induced by IMI was partially antagonized by a dose of methysergide ineffective in modifying AMP pecking. Neither phentolamine nor propranolol blocked IMI pecking. Serotonin was further implicated in IMI pecking in a third experiment, whether chronic PCPA pretreatment significantly decreased IMI, but not AMP pecking. These data suggest that aggressive pecking induced by AMP and IMI may be mediated by different amine systems.