2 male and 17 female patients with hypoparathyroidism including 7 idiopathic, 11 surgical and 1 pseudohypoparathyroidism received 1 alpha-OHD3 at a mean daily dose of 2.7 +/- 0.7 microgram (1.5-4.0 micrograms) combining with calcium 1 g for 14 weeks. The mean age of the patients was 37 +/- 9 old years and the mean course of disease was 15 +/- 10 years. The symptoms and signs of hypocalcium disappeared in 1-3 weeks after therapy, meanwhile the serum ionized calcium (Ca++) and total calcium (TCa) increased from 0.84 +/- 0.02 to 1.03 +/- 0.01 mmol/L and from 6.90 +/- 0.22 to 8.70 +/- 0.20 mg/dl (P less than 0.001) respectively. The serum Ca++ and TCa increased to normal volume in 58% and 63% patients respectively. The concentration of serum 1,25 (OH)2 D3 elevated significantly from 19.5 +/- 1.1 to 29.1 +/- 2.4 pg/ml (P less than 0.01 n = 17). The lever of urinary hydroxyproline was no significant change. The serum phosphate reduced markedly from 5.50 +/- 0.2 to 4.80 +/- 0.2 mg/dl (P less than 0.01). The serum Ca++ and TCa changed to the primitive level when we stopped to use 1 alpha-OHD3 alone for 1-3 weeks. No significant side effects were found. It might be suggested that 1 alpha-OHD3 is effective and safe in treating hypoparathyroidism because calcium absorption in intestine is promoted by 1 alpha-OHD3.