In two patients suffering from hypoparathyroidism (HP) whose serum calcium and -phosphate could not be normalized with Vitamin D3-resp. Calcitriol and who continued to have tetanic convulsions, synthetic 1-38 human parathyroid hormone (1-38 hPTH) was used for treatment. In both patients the intravenous administration of 1-38 hPTH provoked a rapid increase of phosphaturia and cAMP-excretion and an increase of the serum calcium level into the normal range. The same effects, only slightly delayed, could be achieved with subcutaneous injections which the patients had learned to do themselves. In case 1, a boy aged 14 years with autoimmune-HP, the daily administration of 8.5 U/kg BW caused hypercalcemia on the 6th day of treatment; therefore the dosis was reduced to alternate day administration. In case 2, a girl aged 17 1/2 years with idiopathic HP, treatment was started with alternate day administration (7.7 U/kg BW/day of injection); serum calcium increased to levels of about 2.2 mmol/1. Side effects could not be seen. Case 1, however, developed resistance to 1-38 hPTH after 10 weeks of therapy. 1-38 hPTH can be classified as an effective substance in the treatment of HP. Optimal dose and frequency of administration cannot yet be pointed out.