Several alkaloids of the beta-carboline group were tested for their subjective effects in man, and it was found that six of them are hallucinogenic: 6-methoxy harman, 6-methoxy harmalan, 6-methoxy tetrahydroharman, and the corresponding 6-methoxy compounds. Since 6-methoxy tetrahydroharman has been shown to be synthesized in vivo and 6-methoxy harmalan has been postulated as a normal pineal metabolite, it is suggested that such substances may be involved in the causation of altered states of consciousness, either schizophrenic or of a mystical quality.