The objective of the experiment was to investigate the effect of clinoptilolite (a natural zeolite) supplementation in the ration of dairy cows on serum beta-carotene, vitamins A and E concentrations. Fifty-two clinically healthy Holstein cows were randomly assigned to one of three groups according to their age and parity. The first group (group A, n = 17), was offered a concentrate feed supplemented with 1.25% clinoptilolite. The second group (group B, n = 17), was offered a concentrate feed supplemented with 2.5% clinoptilolite. The third group (group C, n = 18), which served as controls, was offered the same concentrate feed without clinoptilolite supplementation. All cows were fed the above concentrates continuously starting 30 days before the expected parturition up to the end of lactation. Blood samples from individual animals were collected just before the start of experiment, at the day of calving and, thereafter, at monthly intervals. All samples were tested for serum beta-carotene, vitamins A and E concentrations. The results showed that the 1.25 and 2.5% supplementation of clinoptilolite had no adverse effect on serum concentrations of beta-carotene, vitamins A and E.