The protective effects of carbamazepine (CBZ) were studied in mice inoculated with Lewis Lung Carcinoma (3LL), Madison Lung Carcinoma (M109), L5178Y lymphoma, L1210 leukaemia and Candida albicans. There was no significant increase in survival time of mice treated with CBZ. However, CBZ, as well as its metabolite CBZ 10-11 epoxide (CBZ 10-11 EPOX), showed a significant increase in NK-cell activity. CBZ also produced a significant increase of phagocytosis and killing properties of PMNs. There was no significant difference in the stimulation of splenic lymphocyte blastogenesis by different concentrations of phytohaemagglutinina (PHA), observed between the controls and CBZ treated mice. The results demonstrate that the effect of chronic treatment with CBZ on the immune response is a complex phenomenon which remains a challenge for future research.