Our studies showed that the chelidonine administered intraperitoneally (ip) exerted an inhibitory effect on the central nervous system of the rodents. It was shown that chelidonine depressed the spontaneous and explorative motor activities, decreased body temperature, potentiated the action of hypnotics and increased sedation in reserpinized mice. Chelidonine did not affect the reactivity of the mice in the hot-plate test, and was without any protective effect against pentylenetetrazol-induced seizures. This alkaloid antagonized the head twitch response induced by 5-hydroxytryptophan (5-HTP) or 5-methoxytryptamine (5-MT) in the rat.