Reproductive wastage in cattle is largely the result of fertilisation failure and early embryo loss (Sreenan et al., 2001). Oviduct fluid forms the environment in which the oocyte and spermatozoa undergo final changes before fertilization and the early embryo develops. However, while oviduct fluid is partly a transudate of blood plasma little is known of its biochemical composition and especially the concentration of energy substrates essential for early embryo development. The objective of this study was to measure the comparative concentrations of glucose, lactate and pyruvate in cattle oviduct fluid and blood plasma on different days of the oestrous cycle.