In 1959 remission occurred in a case of mycosis fungoides following the topical application of mechlorethamine hydrochloride (a nitrogen mustard) to the lesions.1 Since then, mechlorethamine has been used topically in additional cases of mycosis fungoides and to treat several other dermatologic disorders. The results obtained in 29 cases treated by this method at the Cleveland Clinic are examined here to assess the action and the usefulness of topical nitrogen mustard. Method The contents of one 10 mg. vial of mechlorethamine hydrochloride* was dissolved in 50 ml. of normal saline at room temperature. This made a 20 mg. % solution. Since degradation occurs rapidly, this mechlorethamine solution was applied to the skin immediately after mixing. The skin was clean and free of ointments. If the lesions being treated were small and discrete, they were covered with a piece of gauze moistened with mechlorethamine solution. If the lesions were more extensive,