This study aimed to assess the validity and interpretation of the spot test for monitoring dapsone self-administration that employs filter paper impregnated with a modified Ehrlich''s reagent. Urine specimens obtained from 20 volunteers, who took 100 mg dapsone for four days in succession, were investigated by this test. Findings indicate that spot tests will be negative after an average of three missed doses of dapsone, if compared with a standard of 5 .mu. dapsone per ml of urine. No negative spots are expected in fully compliant patients, and no positive spots are expected in patients who did not take dapsone for a week or longer. In the context of the treatment goal, it is argued that this degree of sensitivity makes the spot test a valid tool for the monitoring and management of patient compliance in leprosy control programs.