Profound hyperuricemia (19-42 (27 +/- 3.3) mg/dl) was noted in seven adult patients with volume depletion and marked prerenal azotemia (SUN, 155 +/- 30 mg/dl and serum creatinine 5.2 +/- 1.1 mg/dl). The serum level of uric acid returned to normal following the administration of 3.2 +/- 0.4 liters of saline/day over a period of 3.4 +/- 0.6 days. Throughout the course of the illness, there were significant correlations (r = 0.83, p less than 0.01) between the serum levels of both urea nitrogen and creatinine and those of uric acid. Because of the rapid reversibility of this hyperuricemia with hydration, it should be differentiated from other clinical conditions associated with acute renal failure and profound hyperuricemia.