Cocaine stimulated the early careers of two brilliant investigators, Sigmund Freud and Sherlock Holmes. In fact, their common attraction to the euphoric properties of the coca leaf may be more than a coincidence. But whatever the Freud-Holmes relationship, the cocaine episodes in each of their lives reflect the impact of a new psychic drug on literature and science. Some of their admirers may deny or overlook this aspect of their careers, thinking that any association with such a drug can only be an embarrassment. But the international enthusiasm for cocaine which antedated and extended beyond their periods of endorsement makes it unlikely that any fair-minded person will censure them. The cocaine episode illustrates how easily objective evaluation may be submerged by personal enthusiasm and how remarkably difficult it may be, in spite of vast amounts of evidence, to judge correctly a widely used drug. Perhaps a reason for delay in