The feed of weaned piglets of Hungarian Large White X Duroc and Dutch Landrace X Duroc genotype was supplemented with 0.5 mg selenium, 50, 100 or 150 mg vitamin E, and 2.5 or 5 mg riboflavin per kg. Feed supplementation enhanced the cytotoxic reaction and elevated the antibody titres produced against purified horse gamma globulin antigen. However, as compared to the control the differences were not significant. Feed supplementation exerted a beneficial, though varying, influence on the indices of cell-mediated immunity. The proportion of rosette-forming cells and blastogenic transformation induced by specific (horse globulin) and nonspecific (phytohaemagglutinin, PHA) mitogens underwent the most expressed and most significant increase in pigs fed 5 mg selenium, 100 mg vitamin E and 5 mg riboflavin per kg of feed. On the other hand, feed supplementation failed to enhance the responsiveness to intradermal PHA (type IV allergic reaction).