T cell subset distribution and anti-M. leprae specific antibody levels were followed in leprosy patients during polychemotherapy (or multidrug therapy, MDT). Before treatment, the T cell subset counts showed that the multibacillary patients (28) have a significant decrease (p less than 0.05) in the CD3+, CD4+ T percentages and CD4+/CD8+ ratio as compared to the healthy controls (96). The paucibacillary patients (30) had no significant T cell disturbances. An ELISA test has been developed using the natural trisaccharide-ocytl-BSA (NTO) antigen to identify specific IgM antibodies (IgM anti-T). Multibacillary patients (22) showed higher antibody titers than paucibacillary patients (11). But the IgM anti-T levels of the two groups are significantly higher than controls belonging to the same ethnic group. A daily polychemotherapy (Dapsone, Rifampicine, Clofazimine) was done for 6 months in paucibacillary patients and 2 years in multibacillary patients according to the leprosy group study recommendations (Prof. Grosset, Hôptical de la Salpêtrière, Paris, France). A normalization of the CD4+ T cells was obtained by a 6 month therapy in multibacillary patients and a significant decrease in the IgM anti-levels was obtained during polychemotherapy in multibacillaries (p less than 0.001) and paucibacillaries (p less than 0.05).