Concentrations of plasma copper, plasma zinc and blood selenium in sheep, goats and cattle, grazing together on natural pastures, were determined at two- to three-monthly intervals over a two-year period. Cattle had the lowest plasma copper concentrations, but no definite differences in plasma zinc concentrations between species could be found. Sheep had higher blood selenium concentrations than goats, with those of cattle being the lowest. Regression analyses within species indicated that blood selenium concentration was related to gluthatione-peroxidase activity, although correlations were generally too low for predictive purposes (r ≤ -0,61). Distinct differences were found between species when blood selenium concentration was related to the haematocrit.