The effects of i.v. N,N-dimethyltryptamine (DMT) were studied on arterial blood pressure, rectal temperature, pupil size and the electroencephalogram of the rabbit. DMT altered these parameters in a dose-related manner causing increased blood pressure, hyperthermia, pupilary mydriasis and activation of the electroencephalogram. Pretreatment with the monoamine oxidase inhibitor, iproniazid, prolonged the effects of DMT, while pretreatment with chlorpromazine or methiothepin attenuated these actions of DMT.