Kidney tissue calcium content from 33 diagnostic human renal biopsies was measured to assess tissue calcium concentration early in the course of human renal disease. Renal calcium content was correlated significantly with serum creatinine (r = 0.71, P < 0.001), serum phosphate (r = 0.64, P < 0.001), and serum Ca x P product (r = 0.66, P < 0.001), but not with serum calcium (r = -0.17, P > 0.05). Threefold greater calcium content was measured in biopsied tissue than in normal renal tissue (315 +/- 169 vs 69 +/- 17 mg/kg renal tissue, P < 0.001). The mean level of serum phosphate and Ca x P product was higher in the patients with significant renal function impairment (Ser > 115 mumol/L) than in patients with normal renal function (1.76 +/- 0.33 mmol/L vs 1.29 +/- 0.18 mmol/L, P < 0.001; 43 +/- 4.7 vs 33 +/- 4.5 mmol 2/L2, P < 0.001, respectively). The mean serum calcium levels were not different in the two groups (1.97 +/- 0.24 mmol/L vs 2.07 +/- 0.16 mmol/L, P > 0.05). The results suggest that renal calcium deposition begins early in the course of various renal diseases, and hence may accelerate progression of chronic renal failure the severity of renal calcium deposition is correlated with hyperphosphatemia and with the level of renal impairment. Dietary phosphate restriction may be necessary early in the course of renal disease.