The effect of parathyroid hormone on calcium and phosphate metabolism have been widely investigated, however less attention has been paid to the effect on urinary excretion. This study was performed for the purpose determining urinary excretion of Na, K, Ca, and Po₄, of 18 thyroparathyroidectomized (TPTX) rabbits, which were TPTX previously 7 to 10 days compared with the same normal ones. After TPTX 0.2 mg/day of synthyroid was donated to the rabbits. The concentration of electrolytes in the serum and urine was determined by the following method; Na and K were determined by means of flame photometry, Ca was by EDTA titration method, and Po₄ by Fiske and Subba-Raw method. The results as follows. The concentrations of electrolytes in the serum were 1) In the normal control rabbits (N = 25) (data, Mean±S.E.) Na 131.72±1.33 mEq/L, K 3.59±0.28 mEq/L, Ca 12.58±0.29 mg%, Po₄ 4.50± 0.45mg%. 2) In the TPTX rabbits(N= 18) Na 140.6l±2.56 mEq/L, K 3.38±0.36 mEq/L, Ca l2.18±0.45 mg%, Po₄ 3.92± 0.35 mg%. There was no significant change between the normal and TPTX rabbits. The concentration of elelctrolytes in the urine were variously changed. 3) In the normal rabbits. Na 8.40±1.09 mEq/L, K 81.59±10.19 mEq/L, Ca 16.02±3.12 mg%, Po₄ 13.16±2.89mg%. 4) In the TPTX rabbits, Na 14.57±3.39 mEq/L slight ncreased, K 116.06±12.77 mEq/L significant increased (P<0.05), Ca 18.90±5.44 mg% no significant increased, Po₄ 43.38±8.67 mg% significant increased (p<0.01). The effect of TPTX was assumed that it affected upon increasing tubular secretion of K⁺ and inhibition of the tubular reabsorption of Po₄.