The aim of this study was to evaluate the effect of calcitriol treatment on glucose intolerance in uraemia. Thirty one patients on haemodialysis who had never been treated with vitamin D or related drugs, and 12 healthy control subjects with normal renal functions were studied. Uraemic patients were randomly divided into two groups; 16 patients were treated with oral calcitriol (0.5 micrograms/day) for 8 weeks, and 15 uraemic patients and 12 healthy subjects were given a placebo. In all these cases, before and 8 weeks after treatment, baseline serum glucose, insulin, calcium, parathormone (PTH), and 1,25 (OH)2D3 were measured. After an oral load of 75 g glucose, blood glucose and insulin were determined at 30, 60, 90, and 120 min. The same measurements were repeated after 8 weeks. HbA1c and fructosamine were also measured at 0 and 8 weeks. Baseline serum insulin was significantly elevated after calcitriol treatment (7.81 versus 11.63 microIU/ml) there was also a significant increase in insulin following calcitriol treatment at 30, 60, 90, and 120 min. On the other hand, glycosylated haemoglobin (HbA1c) and fructosamine decreased after calcitriol treatment (HbA1c 7.09% versus 5.22% P < 0.01 and fructosamine 2.92 versus 2.50 mmol/l P < 0.01). Blood glucose significantly decreased after calcitriol treatment at 0, 30, 60, 90, and 120 min. In the other two groups there were no significant changes in any parameters. These results seem to confirm that vitamin D influences pancreatic beta (beta) cell secretion and suggest that calcitriol may improve glucose intolerance in uraemic haemodialysis patients.(ABSTRACT TRUNCATED AT 250 WORDS)