Twenty-five yearling wethers, weighing 45 to 50 kg, were used in a trial designed to compare the bioavailability of dl-alpha-tocopheryl acetate (TA) and d-alpha-tocopheryl polyethylene glycol-1000 succinate (TPGS). The sheep, five per treatment, were each given a basal diet without vitamin E supplement (control) or with a daily oral supplement of 240 iu TA or TPGS, or of 480 iu TA or TPGS. Blood samples were obtained at zero time, and then twice daily for three weeks. The bioavailability was greater for TA than for TPGS. This was indicated by the significantly higher (P less than 0.01) plasma alpha-tocopherol concentrations during the three-week experimental period in sheep dosed with equivalent units of TA than in those dosed with TPGS. When administered at 480 iu, the TPGS produced plasma profiles similar to those found after administration of the lower (240 iu) dose of the TA.