In this field study serum selenium concentrations of 340 cows on 14 dairy farms in Upper Austria were determined. Therefore serum samples were taken twice from each cow: first during dry period (4 - 2 weeks a.p.) and a second time during lactation (4 - 6 weeks p.p.). The projected intercalving interval was used as fertility parameter for cows diagnosed pregnant. Aim of this investigation was to evaluate selenium status of dairy cows, to get information on seasonal variations in serum selenium contents and to find out, if there are correlations between projected intercalving interval and selenium status. Mean selenium concentrations before calving were about one third lower than after calving. During the dry period serum selenium contents of 267 cows (79%) were below 40 mug/l, 68 (20%) were between 40 and 70 mug/l and 5 (1%) were higher than 70 mug/l. In stage of lactation 150 cows (44%) had concentrations below 40 mug/l, 150 (44%) lay between 40 and 70 mug/l and 40 (12%) were higher than 70 mug/l. Highest selenium contents before calving were found in October, while there were no seasonal variations in selenium after calving. Correlations between projected intercalving interval and selenium status could not be found. The rise of selenium concentrations after calving is explained by concentrates enriched in selenium, which are mostly given during lactation. The rather low selenium status found in this study is confirmed by other investigations of Austria, Germany and Switzerland. In spite of the very low selenium concentrations the cows show satisfactory fertility and milk production and no increased incidence of other disorders. Standard values of blood selenium concentrations found in literature are considered to be too high for the specific situation in Austria.