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Embryonic losses contribute considerably to low pregnancy rates. Between d 8 and 17 after breeding, the conceptus secretes interferon-τ as a mechanism for maternal recognition of pregnancy and maintenance of the corpus luteum. Nonsteroidal antiinflammatory drugs inhibit the synthesis of prostaglandin F(2α) by suppressing the enzyme cyclooxygenase. Flunixin meglumine (FM) has been demonstrated to delay luteolysis and to support embryonic survival. The objective of this study was to evaluate the effect of FM and carprofen on conception rates in dairy heifers and cows, respectively. In experiment 1, the effect of FM on pregnancy rates and progesterone concentrations in dairy heifers was tested. A total of 391 heifers were randomly assigned to 1 of 2 groups. Heifers in the treatment group (n=197) received 2.2 mg of FM i.m./kg of body weight twice on d 14/15 and 15/16 after insemination, whereas heifers in the control group (n=194) remained untreated. Blood samples from 388 heifers were taken on d 14/15 and 21/22 after artificial insemination and analyzed for progesterone. Pregnancy rates were 58.2 and 54.8% for the control and treatment groups, respectively. Mean progesterone concentrations were not affected by treatment and number of artificial insemination service (first or second artificial insemination service), but were affected by time and time × pregnancy status. In experiment 2, the objective was to verify the effects of carprofen, a longer acting nonsteroidal antiinflammatory drug and to evaluate its effect on conception rate to first service in dairy cows. A total of 380 cows were randomly assigned to 1 of 2 treatment groups. Cows in the treatment group (n=194) received 1.4 mg of carprofen s.c./kg of body weight on d 15 after insemination, whereas cows in the control group (n=186) remained untreated. Pregnancy was diagnosed between d 40 and 47 after insemination. Conception rates to first service were 35.5 and 33.0% in the control and treatment groups, respectively. Neither flunixin meglumine nor carprofen improved conception rates to first service in dairy cattle in the dosage and administration schedule tested.