Four μg of 1α-OH-D3 were given orally every other day to 10 uremic patients (8 on chronic hemodialysis) for 1–12 weeks and 200 μg of 25-OH-D3 to 3 patients on chronic hemodialysis for 4–8 weeks. Before and at the end of therapy a transilial bone biopsy was analysed. Serial evaluations of serum immunoreactive PTH (P.iPTH), calsium, phosphate and alkaline phosphatase were made. It is concluded that both 1α-OH-D3 and 25-OH-D3 (this latter, however, at a dose 50 times higher) are able to depress hyperparathyroidism in 2/3 of the cases and to improve consistently the defect of mineralisation. Neither PiPTH nor the bone histomorphometric parameters returned to normal in any case, so that long-term evaluation of these 2 drugs in warranted.