Serum gamma glutamyl transferase (GGT) levels in blood samples taken from normal lambs which had suckled colostrum were found to be up to 140 times normal adult levels. These high serum levels declined rapidly reaching a stable level approximately 60% higher than normal adult values by 24 days of age. Newborn lambs which had not yet consumed colostrum had GGT levels which would be considered normal in adult sheep. The GGT concentration in ewes' colostrum was up to 470 times normal serum levels. There was a significant positive correlation between serum GGT and gamma globulin levels in blood samples taken from lambs within 24 hours of birth.