Plasma levels of 25-OH-D, 1,25-(OH)2-D and 24,25-(OH)2-D in acute renal failure, chronic glomerulonephritis and chronic renal failure were determined by competitive protein binding assay and evaluated for the correlation with the degree of renal impairment and the influence of dialysis, renal transplantation and the administration of vitamin D and 1-alpha-OH-D3. In this study it is revealed that 25-OH-D deficiency could be normalized by the administration of vitamin D2. Plasma levels of 1,25-(OH)2-D are decreased in proportion to the degree of renal impairment and it is clearly depressed in patients, with a Ccr of 30 ml/min or less. Although biosynthesis of 24,25-(OH)2-D is not remarkably depressed, it is necessary to resolve various questions including the methods of measurement in this respect. It is also disclosed in the present study that 1-alpha-OH-D3 is faster in action than vitamin D2 when used to correct 1,25-(OH)2-D3 deficiency.