Twenty-eight subjects, matched by sex and Cannabis experience, received by controlled inhalation under single- and double-blind conditions 600 mg marihuana placebo and marihuana. Forearm, venous and arterial pressures, forearm blood flow, and heart rate were recorded while supine. Derived functions such as "dp/dt", regional arterial resistance, and venous compliance were calculated from these variables. (1) Placebo produced no intoxication or consistent physiological responses. (2) Marihuana produced intoxication in all Cannabis-experienced and half the non-experienced subjects. (3) Cardiovascular responses occurred in response to marihuana in the absence of intoxication, indicating that they were not psychogenically mediated. (4) Inhibition of vagal tone may contribute to the tachycardia seen with marihuana. (5) Reflexly mediated sympathetic responses may be muted in the presence of marihuana.