Oral zinc was tried in 15 cases of multibacillary leprosy as an immunostimulant in addition to conventional antileprosy drugs. Results were compared with those in ten similar cases treated with dapsone alone. Cases treated with zinc showed faster clinical improvement, regrowth of eyebrows, rapid fall in the bacterial index (BI) and in the bacterial index in the granuloma (BIG), early and greater influx in lymphocytes in the granuloma, and neovascularization. Upgrading occurred in 6 out of 15 patients taking zinc, but in only 1 out of 10 patients in the control group. Five out of six patients who showed upgrading in the treated group became lepromin positive. Only one patient (BL) showed lepromin conversion in the control group.