Effects of acute and chronic stresses (exercise, cold, and immobilization) on gamma-glutamyltransferase (gamma GT) activity in the rat kidney were investigated. In the extramicrosomal fraction there were significant decreases in acute-exercised rats but significant increases in cold-adapted and immobilized rats. In the microsomal fraction, on the other hand, the gamma GT activity of acute-exercised rats increased definitely. The results suggest that different types of stresses have different effects on gamma GT activity in the rat kidney.