Apomorphine induces a pecking response in pigeons and the effects of various drugs on this pecking response were studied. The pecking induced by apomorphine (1.64 μmole/kg) has a rapid onset, and lasts for approximately 1 hr. Pecking induced by apomorphine can be blocked by dopaminergic receptor-blocking agents such as chlorpromazine, haloperidol, bulbocapnine and morphine, but not by α- or β-adrenergic receptor-blocking agents. Cholinergic agents have an inhibitory effect on pecking. The inhibitory effect of oxotremorine can be reversed by the prior administration of atropine. Apomorphine can induce both pecking and emesis while apomorphine methiodide causes only emesis. This ivestigation indicates that the pecking induced by apomorphine is caused by the stimulation of central dopaminergic receptors and that central cholinergic systems have a modulating effect on pecking. Serotonergic systems might also inhibit the pecking induced by apomorphine.