Cannabis has long been used as an indigenous medicine in the south of Africa, South America, Turkey, Egypt, and many areas of Asia including India, the Malays, Burma, and Siam. The heyday of the medical application of cannabis occurred in the Western world in the period from 1840 to 1900. During this time more than 100 articles were published recommending it for various ailments and discomforts. Physicians of a century ago knew far more about it and were much more interested in exploring its therapeutic potential than are physicians today. While its use was already declining somewhat in the earlier part of this century, primarily because of the introduction of synthetic hypnotics and analgesics, the attendant difficulties imposed on its use by the Tax Act of 1937 completed its medical demise, and it was removed from the U.S. Pharmacopoeia and National Formulary in 1941. Nonetheless, a spate of papers published prior to that time have established for it a compelling potential as a medically useful substance. Some of the indications are only suggestive; some are more definitive; but this potential has yet to be realized, largely because of ignorance on the part of the medical advisory establishment, the bad reputation of cannabis, and the legal difficulties involved in doing the kinds of basic and clinical research that would long since have been stimulated in any other group of substances with such promising possibilities. Despite the extreme difficulties of doing medical research with these drugs, some studies have been completed, and these have, to some extent, confirmed the century- old promise of the medical utility of cannabis products. With the relaxation of the restrictions on research and the chemical manipulation of the various cannabinol derivatives, this potential will doubtless eventually be realized.