Eight [male][male] and 1 [female] were given sulfanilamide to maintain a mean blood conc. of 9 mg. %, of whom only 2 completed a 6-week course of treatment. The other 7 were hospitalized for drug fever, 4; neuritis, dermatitis and hepatitis, 1 each. After 2 months'' rest, 6 of these patients and 11 others were given sulfanilamide to maintain a mean blood conc. of 5 mg. %; 6 completed a 92-day course. 12 were hospitalized for toxic reactions or fever, and medication was discontinued in 11 of these. Of the combined group of 20, 6 showed improvement in leprous lesions, 2 showed no acceleration of improvement, 1 was stationary and 10 showed slight progression of leprosy. Toxic complications were more frequent than in treatment of other diseases, perhaps due to lepra reaction. The blood picture was disturbed, with eosinophilia in half the patients. Sulfanilamide is considered effective in treatment of secondary infections complicating leprosy, but ineffective vs. macular or lepromatous leprous lesions.