Sixty clinically healthy Holstein cows were randomly assigned to one of four groups according to their age and parity and vaccinated in late pregnancy (day 190) with a multivalent vaccine against Escherichia coli. The 15 cows in the first group (SeE) were injected intramuscularly with a solution of sodium selenite (0.1 mg Se/kg bodyweight) and vitamin E (alpha-tocopherol acetate, 8 U/kg bodyweight), the cows in the second group (Se) received only selenium and the cows in the third group (E) received only vitamin E at the same doses and by the same route of administration; the cows in the fourth group were used as controls. The vaccination and the injections of selenium and vitamin E were repeated 42 days later. The concentration of selenium in whole blood and of vitamin E in serum was determined by fluorometric methods. Specific antibody titres against E coli were determined in serum samples by ELISA. The results showed that the injection of selenium either alone or in combination with vitamin E significantly improved the production of specific antibodies against E coli, and that the production of specific antibodies was greater after the administration of selenium alone.