A study has been made of possible interrelationships between circulating vitamin A concentration and indicators of altered calcium homeostasis in 31 patients with stable chronic renal failure. Plasma retinol concentrations were high, possibly as a result of increased retinol-binding-protein concentrations secondary to renal failure. There was no correlation between retinol concentration and any other measurement, including vitamin A intake. However, there were significant correlations between plasma parathyroid hormone and calcium, phosphate, alkaline phosphatase, urea, and creatinine concentrations; and those patients with radiological sub-periosteal erosions tended to have the highest concentrations of circulating parathyroid hormone. Our data give no support to the contention that vitamin A status has any bearing on the progression and severity of the hyperparathyroid bone disease of renal failure.