This study was performed to assess the effect of inosiplex(ISP) on the resistance of mice Candida albicans infection, the migration of chicken leukocytes, the production of leukocyte migration inhibitory factor(LIF), and the cell-mediated immunity(CMI) to lepomin in multibacillary lepromatous leprosy patients. The treatment with ISP before or on the time of infection with C. albicans had no or deliterious effect, and treatment with ISP after infection had no effect on the recovery of C. albicans from the kidneys of mice. The migratory ability of chicken leukocytes and the production of LIF from splenocytes of mice were not affected by ISP treatment. However, ISP decreased the migration of chicken leukocytes in vitro, and this decrease was dose-dependent. The therapy of lepromatous leprosy patients with ISP for 10 or 30 days clearly showed the increase of the significant positive rate of Mitsuda skin test to lepromin. The immune recovery as a result of the therapy was found to be the best in the group of patients treated for 30 days. This results suggest that (1) the effect of ISP in renal candidiasis can vary depending on the time of treatment relative to infection, (2) ISP can primarily change the migratory ability of chicken leukocytes but does not affect the production of LIF in mice, and (3) the classical therapy combined with ISP can reinforce or restore the defences of lepromatous leprosy patients against Mycobacterium leprae.