Uric acid metabolism was evaluated in 16 Israeli cystic fibrosis patients, all of whom were taking pancreatic enzyme supplements. The findings were compared with those in a recent study of uric acid metabolism in 65 healthy Israeli children. Hyperuricemia of 4.9 +/- 0.2 (SE) mg/dl was found in the cystic fibrosis patients, compared with a normal level of 3.1 +/- 0.2 mg/dl ( P < 0.05). In five patients, 24-h urine collections were assayed and all showed hyperuricosuria. Thirteen patients had high urinary uric acid/creatinine ratios. Hyperuricosuria increased with the age of the patient and when the administered dosage of pancreatic enzyme exceeded 10,000 lipase units/kg body weight. Despite normal levels of serum creatinine and urea, and normal creatinine clearance in the cystic fibrosis patients, risk of future renal damage seems obvious and preventive measures should be considered.