A set of experiments were conducted to evaluate the antibody response, serum vitamin E level, cortisol concentration and performance of pigs weaned at three ages (21, 28 or 35 d) and fed diet containing either 11 or 220 IU/kg diet recommended level of vitamin E. Supplemental dietary vitamin E (220 IU) increased the concentration of serum vitamin E but, did not affect performance, cortisol concentrations or the antibody response. As weaning age increased, weekly performance increased linearly as did cortisol levels. Animals weaned at 35 d age had the largest primary antibody response, but this difference was not observed for the secondary response. A second set of experiments evaluated effects of four dietary vitamin E levels (11, 110, 220 and 550 IU/kg feed) on the humoral and cell-mediated immune response and performance of 4 wk old weanling pigs housed at one of two nursery temperatures (19 or 30°C). Performance was greater for pigs housed at 19°C compared with pigs housed at 30°C, but mitogen stimulation indices of white blood cells, plasma cortisol levels, and antibody titers were similar. Serum and liver vitamin E levels linearly increased with increasing dietary vitamin E level, but performance, cortisol, antibody levels and mitogen induced stimulation indexes were not affected by supplemental vitamin E levels. In the third experiment, sows fed a NRC level of vitamin E demonstrated little fluctuation in serum vitamin E concentration during a 5 wk lactation period. There was a high concentration of vitamin E in colostrum, followed by a sharp decrease in milk vitamin E concentration after the first week of lactation and remained constant for the next four weeks. Piglet serum was initially low in vitamin Eat 1 d of age but increased with time peaking about week 3. These experiments suggest that supplementing dietary vitamin E above the levels recommended by the NRC to baby pigs (which nursed sows fed NRC recommended levels of vitamin E) will not influence cell-mediated or humeral immune response, performance parameters or cortisol levels when pigs were weaned at various ages or exposed to environmental temperature changes. / Doctor of Philosophy