The effects of drugs influencing the function of extrapyramidal system: chlorpromazine (CPZ), halo peridol, amphetamine, and oxotremorine were checked in rats with lesioned MR or DR raphe areas and in animals pretreated with either p-CPA (p-chlorophenylalanine) or LSD, i.e. at impaired functions of the central serotoninergic system. Lesions of the raphe system and pretreatment with either p-CPA or LSD significantly diminished the cataleptogenic effects of both CPZ and haloperidol. The amphetamine-induced stereotyped behaviour was intensified in animals with raphe system lesions, whereas in rats pretreated with p-CPA or LSD the action of amphetamine was diminished. Rats with raphe system lesions showed no change in the tremorogenic action of oxotremorine. In animals pretreated with either p-CPA or LSD the onset of the oxotremorine tremor was even delayed. It is concluded that an intact and functionally unimpaired serotoninergic system is necessary for the cataleptogenic action of neuroleptics.