The authors have investigated the roles of cortisone and calcium on the depressive effects of local anesthetics on the acetylcholine-induced skeletal muscle contraction in frog. The results are as follows. 1. Tetracaine, cocaine, lidocaine and procaine decreased the acetylcholine-induced skeletal muscle contraction. 2. Cortisone increased the depressive effects of local anesthetics on the acetyl-choline-induced skeletal muscle contraction. 3. There was a tendency that in high calcium concentration, the depressive effects of cocaine and lidocaine on acetylcholine-induced skeletal muscle contraction were increased.