We studied the effect of a trace element combination (Béres Drop Plus; BDP) on the immune response of rats, with intact and with injured immune system. Rats were treated with different doses of BDP for 26 days. The immune system was injured by 7.0 Gy whole body gamma irradiation on the first day of BDP treatment. Rats were immunized on the 31st day of the BDP treatment with sheep red blood cells. In the spleen the cell count and the number of antibody producing cells were determined. In the serum the titre of hemolysin was tested. In rats with intact immune system all used doses of BDP induced elevation of the immune response. The moderate high doses were especially effective. In rats with injured immune system the effect was less. Only the 250 microliters/kg body weight dose could elevate the immune response, and the highest (500 microliters/kg) dose reduced the response.