Leprosy patients treated formerly with dapsone monotherapy followed by combined therapy with rifampicin plus dapsone were surveyed for relapse and rifampicin resistance. The relapse rate was significantly low for the 482 multibacillary (MB) patients receiving > 12 months combined therapy compared with the 49 MB cases receiving < 12 months of combined therapy. The relapse rate was related to the duration of dapsone monotherapy prior to combined therapy. The difference in relapse rate in 247 paucibacillary (PB) patients following > 12 months combined therapy was also of significance, compared with the 66 PB cases who had received < 12 months combined therapy. Five strains of M. leprae isolated from relapsed patients were sensitive to rifampicin by mouse foot-pad test and all relapsed patients responded favourably to fixed duration MDT regimen for MB cases.