The effects of 10-week physical training on both the activity and concentration of γ-glutamyltransferase (γ-GT) in plasma were investigated on 7 sedentary healthy male students. The training consisted of running over 5 km, 6 times/week. The maximal oxygen uptake (V̇o(2)max) and 12-min field performance increased significantly after training, from 43.5 and 2,683.7 to 48.1 ml·kg^-1·min^-1 and 2,931.1 m, respectively. After training the resting plasma γ-GT concentration decreased to half, whereas the γ-GT activity did not vary substantially. The training did not affect the response to the V̇o(2)max test of either concentration or activity of γ-GT. These results may suggest that plasma γ-GT concentration is useful as an index of the extent of physical training.