We studied six oliguric patients with rhabdomyolysis-induced acute renal failure. On admission, all had marked hyperphosphatemia and hypocalcemia associated with low levels of 1,25-dihydroxycholecalciferol [1,25(OH)2D]. During the early polyuric phase, moderate hypercalcemia was accompanied by marked elevations in plasma 1,25(OH)2D and persistent elevations in parathyroid hormone (both amino and carboxy terminals). During the late polyuric phase, the levels of serum calcium and 1,25(OH)2D reverted to normal. Thus, in rhabdomyolysis-induced acute renal failure, the hypocalcemia of the oliguric phase may be secondary to decreased synthesis of 1,25(OH)2D; severe hyperphosphatemia may also have a major role. The hypercalcemia of the polyuric phase may be partly due to increased synthesis of 1,25(OH)2D, resulting from the high parathyroid hormone levels and recovery of renal function.