Model experiment was conducted with growing pigs fed diets containing zero or two levels (1 or 2 g/kg) of fermented wheat germ extract (FWGE). In the first part of the experiment (19 days between 49 and 68 days of age) weight gain and feed conversion were tested. The 2^nd part of the experiment (21 days between 68 and 89 days of age) served to measure the effect of FWGE on some compartments of the immune system. In the first part of the experiment supplementation of the starters’ diet with FWGE yielded 7.8 and 14.2% additional daily weight gain in the 1^st and 2^nd experimental groups, respectively (P<0.05). Humoral immune response to purified horse globulin (PHG) antigen was unaffected by the treatment. The blastogenic response of lymphocytes to non specific mitogens (PHA, Con-A, PWM), phagocytic activity and phagocytic index as well as the intradermal PHA test was consistently and significantly enhanced by the treatments