(1) A number of indications and analogies snggest the trial of coal-tar dyes and their derivativ es in leprosy. (2) Intravenous injections of a large number of dyes have been given to 85 patients. (3) A number of these dyes show marked selective concentration in the leprotic lesions, a phenomenon not seen in certain non-leprotic lesions. (4) With trypan blue, brilliant green, fluorescein and perhaps eosin a definite diminution of the external manifestations of leprosy has been observed, accompanied by other signs of clinical improvement. (5) With the other dy es administered no signs of clinical improvement were observed. (6) This report is a study of the immediate reaction of the lesions; we have as yet no knowledge of the later effects of the injection of these dyes. We consider from this preliminary report that further trial and study of these dyes is definitely indicated in the hope that it may lead to further possibilities in the chemotherapy of this disease.