The aim of this study was to evaluate the effects of a combined low-dose therapy of calcitriol and calcium carbonate on bone metabolism in the early phases of chronic renal failure. A 30-month study involving 17 patients with ECRF was made: 6 months of observation were followed by 24 months of therapy (calcitriol 0.25 microgram/day plus calcium carbonate 1 g/day). The most important results were that renal function was stable throughout the study and there was an increase in calcaemia and a decrease in plasma alkaline phosphatase, plasma osteocalcin, plasma PTH and urinary hydroxyproline. We observed a progressive slowing of the rate of loss of appendicular bone density as well as a decrease of osteoblastic and osteoclastic activity and an improvement of bone mineralization. In conclusion, low doses of calcitriol plus calcium carbonate seem to improve the biochemical and bone derangements in early renal failure.