Plasma urea concentrations have been used as a diagnostic tool in the investigation of reproductive performance in cattle. Data were compiled from three recent studies on bovine fertility and a retrospective comparison of plasma urea concentrations was made between those animals that conceived to an insemination or embryo transfer. In studies I and 2 plasma urea concentrations around the time of insemination were determined. Pregnancies were diagnosed using ultrasonography 35 days later. There was no significant difference between the mean plasma urea concentrations around the time of insemination in the cattle subsequently diagnosed pregnant or not pregnant. In study 3, in vitro produced good quality embryos were transferred into three groups of beef heifers. The three groups were allocated to diets of high energy / high urea, high energy / no urea and low energy / high urea. The plasma urea concentrations at the time of embryo transfer were different between the three groups. However, the pregnancy rates 28 days post transfer, were not significantly different between the three groups. This suggests that the previously reported effects of high protein diets on fertility are not solely due to disruptive effects on the uterine environment. The main effect of urea on fertility may be on oocyte development within the follicle. Overall, these results indicate that measurement of plasma urea concentrations in individual animals around the time of insemination or embryo transfer is not a useful predictor of subsequent pregnancy rate.