To the Editor.— In the 19th century, cannabis products were commonly used in the treatment of asthma. 1-3 Smoking marihuana, on the other hand, is associated with bronchitis and other deleterious effects on lung function. 4 The present report deals with acute marihuana effects on pulmonary capacity in nonasthmatic regular marihuana smokers. Method.— Thirty-one healthy men between the ages of 21 and 30 years who had smoked marihuana frequently for at least two years were studied; more than half had smoked marihuana at least once a week for four or more years. About half were cigarette smokers. None had current respiratory complaints or a history of pulmonary disease. Subjects were randomly assigned to a marihuana group (N =15) or placebo group (N = 16). The marihuana contained 1.5% tetrahydrocannabinol (THC), while the placebo consisted of cannabis tobacco with THC removed. The National Institute of Mental Health provided the drug and the placebo.