Studies were made on several groups of Hereford cattle to determine the plasma zinc concentration at various phases of their reproductive life. In nonpregnant heifers a major cause of variation was due to differences between individual animals. Seasonal changes were also evident but little difference was noted in the zinc levels of cattle sampled at particular stages of the oestrous cycle or over a 24-hour period. Following conception, the plasma zinc levels remained relatively constant until late in pregnancy when a decline occurred. A more marked decline occurred during the periparturient period although the trends observed differed between animals that calved normally and those that suffered from dystocia. Samples obtained from calves approximately 24 hours after delivery contained zinc at concentrations of more than double that recorded for their dams.