OBJECTIVE Previous studies have suggested that aipha-DI therapy can cause deterloration In renal functlon. We have, therefore, examlned the long-term effect of l ahydroxyvitamin D, (alpha-D,) administration upon renal function In hypoparathyroid patients. DESIGN This Is a prospective long-term foliow-up study of alpha-D, admlnlstratlon on hypoparathyroid patients at a mean dally dose of 1 pg (range 05-25 pg) durlng a total of 2040 patient-months. PATIENTS Seventeen unselected patients (14 females and 3 males), two wlth primary and 15 wlth post-surgical hypoparathyroidism. RESULTS The rlgnlflcant effect of alpha-D, on serum and urinary calcium was achieved during the first week of treatment and remained stable at the same range during the close follow-up of 2040 patlent-months. No slgniflcant Change was observed In the serum creatlnlne durlng the whole follow-up perlod. Durlng follow-up, five women developed hypercalcluria and one patient developed hypercaicaemla that disappeared when the dose of the drug was reduced or dllcontlnued. CONCLUSIONS From our study we concluded that alpha-DI Is a safe and effective drug in the long-term therapy of hypoparathyroid patients.Hypocalcaemia, hyperphosphataemia and reduced serum immunoreactive parathyroid hormone (imH) and 1.25dihydroxyvitamin D (I,25(OH)zD) concentrations are the main biochemical features of hypoparathyroidism (Balsam ef al.. 1975; Rosen ef d., 1977;Breslau & Pak, 1979).Parathyroid hormone stimulates the conversion of 25hydroxyvitamin D to 1.