We report five female cases of hypouricaemia accompanied by acute viral hepatitis (serum urate 101 +/- 12 mumol/l, mean +/- SD). Their urate clearance was increased to 14.2 +/- 3.4 ml/min during hyperbilirubinaemia but 24-h urate excretion was not elevated (2.09 +/- 0.64 mmol/24 h). No other renal tubular abnormalities were detected. Comparing urate metabolism with that of four cases of inborn renal hypouricaemia, the degree of uricosuria was lower. One patient showed elevation of serum and urinary oxypurine, which normalized with return of a normal blood uric acid level. In all cases, the serum urate returned to normal after improvement of liver function. We suggest that renal uricosuria due to an isolated renal defect of urate transport might contribute to hypouricaemia in these cases but that inhibition of xanthine oxidase activity might also contribute to this phenomenon.