The self-administration of once-weekly dose s of 300 mg D a pso ne (DDS) by leprosy patients in lhe Mwanza region of Tanzania was monitored using the urine-test method described by Ellard er ai. (1974a). DDS/creatinine rat ios were determined on urine samples voided by 65 supervised le prosy patients on each of 7 successive days following the ingestion of 300 mg DDS. The method was then applied to urine sa mples collected by means of surprise visits to the homes of 158 out-patients 2 days after the day on which a 300 mg dose of DDS should have been taken. The extent of DDS self-ad ministration by the out-patienls was estimated by comparing the results with those obtained from controls given supervised DDS doses and from subjects not laking DDS. Significant amounts of DDS were not detected in the urine sa mples collected from 30% of the out-patienls. Furthermore the average DDS/creatinine ratios of lhe urine sa mples of the other out-patients were significantly lower than those from the supervised controls. The implications of these fi ndings to the treatment of leprosy in the Mwanza region and their relevance to olher leprosy conlrol schemes is discussed.