The effect of jugular infusions of glucose and amino acids on activation of p70S6K was studied in the bovine mammary gland. Cows were starved for 22 h to quench milk protein synthesis before resupplying EEA+Glc, Glc, Met+Lys, His, Leu or saline. Results implicate glucose as a regulator of global, rather than ribosomal, protein synthesis. EAA appear to play a far greater role in p70S6K regulation than glucose. His and Leu appear to act as metabolic agents in the mammary epithelial cell; Leu through elevating RNA levels thereby contributing to the long-term protein synthesis capacity, and His through stimulating protein translation.