Serum calcium level was decreased by submaxillary gland removal in rate. To investigate the mechanisms involved in the above change, the authors examined the effects of thyroxine, vitamin D₂, and calcium gluconate, which influence the metabolisms of calcium and submaxillary gland, on the serum calcium level of the intact and submaxillary gland removal rats. The results were as follows: 1) Serum calcium level decreased by submaxillary gland removal. 2) Vitamin D₂, increased the serum calcium level significantly. 3) Thyroxine falied to recover the decreased serum calcium level induced by submaxillary gland removal to the control level. 4) In submaxillary gland removal rats, vitamin D₂ failed to increase the serum calcium level. 5) In thyroxine administered rats for 55 days, of which submaxillary glands were removed, vitamin D₂ failed to increase the serum calcium level. 6) The serum calcium level in intact rats was increased slightly, but increased significantly in submaxillary gland removal rats shortly after intravenous injection of calcium gluconate.