This thesis is an investigation of parenteral vitamin E for the prevention of peripartum disease, and the diagnosis and treatment of endometritis in postpartum dairy cows. Two randomized clinical trials were conducted in commercial dairy herds in eastern Canada. In the first trial, 1142 cows in 21 herds were assigned to receive either a single subcutaneous injection of 3000 IU of vitamin E, or placebo, one week prior to expected calving. Cows with marginal pre-treatment vitamin E status (serum [alpha]-tocopherol <2.5 [mu]g/mg cholesterol) that received an injection of vitamin E tended to have reduced risk of retained placenta. However, in cows with adequate serum vitamin E, there was no reduction in the incidence of any disease. For clinical application, primiparous animals were most likely to benefit from prepartum injection of vitamin E. In the second trial, the reproductive tract of 1910 cows in 27 herds was examined once between 20 and 33 days in milk (DIM), by vaginoscopy and palpation. Survival analysis was used to derive a case definition of endometritis based on factors associated with increased time to pregnancy. The presence of muco-purulent or purulent uterine discharge, or cervical diameter greater than 7.5 cm identified cows with endometritis. The prevalence of endometritis was 16.5%; 44% of these cases were identified by vaginoscopy. No diagnostic criteria based on palpation of the uterus had predictive value for time to pregnancy. Cows with endometritis were randomly assigned to receive an intra-uterine infusion of cephapirin benzathine, an injection of prostaglandin F2[alpha] (PGF2[alpha]), or no treatment. There was no benefit of treatment between 20 and 26 DIM, and a reduction in pregnancy rate in cows that received PGF2[alpha] in the absence of a corpus luteum (CL). Cows treated with cephapirin after 26 DIM had significantly shorter times to pregnancy than untreated cows. The effect of either treatment was enhanced in cows with a CL, whereas there was no benefit of PGF2[alpha] in the absence of a CL.