Holstein cows (n = 104) and heifers (n = 35) were used to determine the effects of treatment with selenium (Se) and vitamin E on whole blood Se values and fertility. At 21 +/- 3 days before parturition, 55 cows and 19 heifers were injected with 680 IU of vitamin E and 50 mg of Se as sodium selenite. Treatment had no effect on days to first estrus, days to first service, days to conception, services per conception, or number of uterine infusions required. Blood samples were obtained from 33 nontreated cows and heifers and 32 treated animals at 21 and 14 days (+/- 3) before calving and at 7 and 14 days (+/- 3) after calving. Mean whole blood Se level at -21 days (day 0 was day of parturition) and before Se-vitamin E treatment was 0.109 micrograms/ml. At days -14, 7, and 14, blood Se was significantly higher in the treated than the non-treated animals. Blood Se was lower on all sampling days in cows calving in July through November than in cows calving in December through April. Heifers in their 1st lactation had lower blood Se concentrations than did cows in their 2nd or later lactation. In feeds sampled at 2-week intervals, mean concentrations of Se in Bahia grass, mixed ryegrass and oats, corn silage, and sorghum silage were less than 0.1 micrograms/g on a dry matter basis. Bermuda grass, alfalfa hay, and concentrates contained greater than 0.1 micrograms of Se/g. Large variation existed in Se concentrations of individual feedstuffs.