A Jersey herd was investigated following a decrease in milk yields. The cattle were permanently housed and fed a complete diet in four groups on the basis of yield. They were generally healthy, but the dry cows and many of the milking cows were over fat. The plasma concentrations of ,β-hydroxybutyrate and glucose were normal, but the activities of aspartate aminotransferase and glutamate dehydrogenase and the concentration of non-esterified fatty acids were high. Fatty liver syndrome was diagnosed. All the dry cows were condition scored and placed into one of three dietary groups according to their score. They were exercised in an outdoor paddock and entered the pre-calving feeding group at least two weeks before calving; 75 per cent of them achieved a condition score of less than 3, and most of them produced normal milk yields. Thirty cows which had developed signs of fatty liver syndrome were paired and one of each pair received an injection of 640 mg of recombinant bovine somatotrophin. The yield of the treated cows was significantly higher (P<0.05) for the first two weeks after the injection. The treated cows had higher plasma concentrations of β-hydroxybutyrate and non-esterified fatty acids and lower plasma urea concentrations seven days after the injection. No other biochemical parameters were affected.