The effects of parathyroidectomy in Rana pipiens are being investigated in our-laboratories. The results of the work being reported demonstrate that the calcium concentration in whole blood and plasma gradually decrease 50 to 60% below the control values within 1 to 2 weeks. However, a hypocalcemia is not permanent as is evidenced by the fact that at the end of 29 weeks the whole blood calcium of the operated animals returned to 8.3 mg.% which approximates the lowest calcium values obtained from unoperated animals. Calcium concentrations in urine taken from the parathyroidectomized animals on different days are 13 to 78% above the control values. These results indicate that in parthyroidectomized frogs there is a loss of calcium through the urinary system which is concomitant with the decrease in plasma calcium. No death from tetany occurred in the operated animals even when their blood or plasma calcium was at its lowest levels. Histological examination of parathyroid glands taken from winter frogs revealed that these glands undergo a degeneration wherein the tissue is highly reticular and the cells appear to be degenerating.