The activities of aspartate aminotransferase (GOT), alanine aminotransferase (GPT), alkaline phosphatase (alkP), creatine kinase (CPK), and ornithine carbamoyltransferase (OCT) were determined in liver, heart, skeletal muscle, brain, kidney, lung, spleen, adrenals, pancreas, thyroid, thymus, and red cells of 56 bovine fetuses varying in gestational age from 115 to 255 days. The tissue aminotransferase activities were the most variable with gestational age. The GPT activity of liver, kidney, spleen, and red cells and the GOT activity of red cells decreased with fetal age. The GPT activity of heart, brain, and skeletal muscle and the GOT activity of adrenal, brain, and skeletal muscle increased with fetal age. Increasing activities were also described for adrenal and brain alkP and for brain and skeletal muscle CPK. In contrast, the OCT activities were fairly constant for each tissue as a function of gestational age.