In 58 patients with end-stage renal failure before commencement of regular hemodialyses treatment (RTD) and 58 patients under RTD bone mineral content (BMC) was determined by the use of the photon absorptiometry. Further the effect of a treatment with bitamin D3 and 5,6-trans-25-OH-vitamin D3 on BMC was studied. There existed a negative correlation between the duration of chronic renal failure or of RDT as well as of the serum parathyroid hormone level to BMC. No correlation was found between BMC and serum calcium level. During a 14 months-course treatment with vitamin D3 or 5,6-trans-25-OH-vitamin D3 BMC increased. The method of photon absorptiometry presented itself as an easy and well reproducible technique for routine examinations.