To the Editor.— Kornhaber's communication ( 215 :1988, 1971) on marihuana use by adolescents succinctly and eloquently corroborates my own experiences and conclusions, item by item, sentence by sentence. My impression (and at this stage of our research all we have to go on is impressions) is that marihuana is a dangerous, toxic drug in precisely the ways that Kornhaber describes; as he points out, these are such subtle, quantitative deviations from normal adolescence as to be nearly undetectable by simplistic psychological tests, and certainly impossible to be perceived subjectively by the drug user himself. The marihuana user has an obvious vested interest in finding the drug harmless; this interest is compounded, in my experience, by an underlying terror that he has been permanently damaged. The kind of research that will verify our impressions must be longitudinal, statistical, and therefore slow. In the meantime we owe it to our profession and