Analysis of computerized data compiled according to the OMSLEP system in the leprosy control service in Guadeloupe has shown that from 1970 to 1984, 80% of the patients were detected by passive case-finding (symptomatic patients), 10% by active case-finding among the school population and 10% by active case-finding among the house-hold contacts of known patients. During the same period of time, global incidence of new cases of leprosy declined from 24 to 11 per 100,000 inhabitants. The decline was greater for paucibacillary cases (y = -0,94) than for multibacillary cases (y = -0,45), and much greater among persons under 15 years of age (y = -3,22) than among those older ones (y = -0,67). Simultaneously 118 relapses, an annual incidence of 1,3%, were observed among the multibacillary patients previously treated by dapsone monotherapy for five years or more. All cases the biopsies of whom were inoculated for drug sensitivity testing in the mouse foot pad yielded dapsone-resistant M. leprae. The proportions of relapses among the annual sources of infection increased from 16% in 1970 to 47% in 1984. Chemoprophylaxis of relapses among multibacillary patients already treated for more than five years with dapsone monotherapy is one of the priorities for leprosy control in Guadeloupe.