The effects of daily supplementation of 1000 IU of d-α- or dl-α-tocopherol acetate to Holstein cows from drying off to 8 wk after calving were studied 1) to compare the bioavailability of d-α- and dl-α-tocopherol acetate by monitoring vitamin E concentrations in plasma, red blood cells, and neutrophils and 2) to determine the effect of d-α- and dl-α-tocopherol acetate supplementation on O2− and H 2 O 2 release by neutrophils. Supplementation with d-α- or dl-α-tocopherol acetate increased vitamin E concentrations in blood plasma, red blood cells, and neutrophils; the d-α form was more effective than was the dl-α form. Supplementation with d-α- or dl-α-tocopherol acetate had no effect on the release of O2− and H 2 O 2 by neutrophils, suggesting no harmful effects on surrounding tissues from oxygen-free radicals produced by neutrophils.