A group of 220 patients with mycosis fungoides (MF) and other lymphomatous diseases was treated with sustained topical applications of dilute aqueous solutions of mechlorethamine hydrochloride for intervals ranging in excess of seven years. Response to treatment, immunologic responsiveness, and subsequent course and survival were inversely related to magnitude of disease at time of starting treatment. Relapses were common and in most instances were related to failure to maintenance of topical therapy rather than to drug resistance. In selected patients topical therapy with an analog of mechlorethamine (nor-mechlorethamine) and with topical immunogenic agents provided additional improvement.