The possible involvement of the pituitary-adrenocortical axis with severe pre- and post partum udder oedema was studied in a herd of 60 Holstein/Friesian cows. The prevalence of udder oedema in this herd was about 75 per cent. The animals were fed a diet containing high levels of potassium (average daily potassium intake 410 g per cow). The concentrations of sodium, potassium, chloride and total protein in the plasma of the cows were within their normal ranges. In one animal a very low plasma cortisol concentration (2.30 ng/ml) was accompanied by normal plasma glucose and beta-hydroxybutyrate concentrations. The adrenal responsiveness of two heifers with severe udder oedema was impaired one month after parturition in comparison with 11 normal animals (increases from 3.27 to 38.8 and 23.2 to 37.8 ng cortisol/ml compared with 8.02 +/- 1.19 to 146 +/- 16.7 ng cortisol/ml but returned to normal spontaneously after 175 days. One cow was diagnosed as having primary adrenocortical insufficiency.