Gentled rats injected subcutaneously with glucagon (20 µg/ 100 g body weight) showed a significant decrease in plasma growth hormone (GH) at 15 min after glucagon injection. A subcutaneous injection of 50 % glucose did not cause the early suppression as shown at 15 min after glucagon injection, but at 30 min after glucose injection a tendency to decrease in plasma GH was observed. In urethane anesthetized rats, a subcutaneous administration of glucagon (1µg or 10 µg/100 g body weight) failed to elicit an increase in plasma GH. In vitro incubation of anterior pituitary fragments with glucagon failed to decrease the release of GH, suggesting that glucagon does not act directly on the anterior pituitary. The findings of this study in rats suggest that glucagon may inhibit GH secretion.