The paper derives from research conducted in New York City under the auspices of the Mayor's Committee on Marijuana. Studies were conducted of the effect of marijuana on a series of 77 subjects, including some who had previously used marijuana for varying periods of time. This paper consists primarily of a description of the psychiatric manifestations caused by the drug. The findings suggest that marijuana is taken by its users for the purpose of producing sensations comparable to those produced by alcohol. It causes a lowering of inhibitions comparable to that elicited by alcohol in a blood concentration of 2-3 mg. The user may speak and act more freely, is inclined to daydream, and experiences a feeling of calm and pleasurable relaxation. Marijuana, by virtue of its property of lowering inhibitions, accentuates all traits of personality, both those harmful and those beneficial. It does not impel its user to take spontaneous action, but it may make the user's response to stimuli more emphatic than normally. Increasingly larger doses of marijuana are not necessary for the long-term user to capture the original degree of pleasure. Marijuana, like alcohol, does not alter the basic personality, but by relaxing inhibitions may permit antisocial tendencies formerly suppressed to come to the fore. Marijuana does not in itself produce antisocial behavior. There is no evidence to indicate that continued use of marijuana is a stepping-stone to the use of opiates. Prolonged use of the drug does not lead to physical, mental, or moral degeneration, nor is there any evidence of any permanent deleterious effects from its continued use. Quite the contrary, marijuana and its derivatives and allied synthetics have potentially valuable therapeutic applications that merit future investigation. 3-item bibliography