Using a trial design previously evolved at Sungei Buloh Leprosarium, a pilot trial was performed of B.663, in the dosage of 100 mgm. twice weekly, in eight patients with previously untreated lepromatous leprosy. The therapeutic results, as measured by clinical, bacteriologic and histologic assessment, and especially by the rate of fall of the morphologic index, were similar to those obtained with sulfone therapy or with 0.663 in the dosage of 300 mgm. daily. Although B.663 pigmentation was produced in all eight patients, it developed more slowly and was less intense than with standard dosage. Difficulties resulting from skin discoloration in assessing the clinical progress of patients on B.663 are discussed.