A Jewish Iraqi woman with familial isolated renal tubular uricosuria, urate clearance of 60.5 +/- 5.7 ml/min and hypouricemia of 1.0 +/- 0.2 mg/dl is described. The combined pyrazinamide-probenecid test suggested a presecretory defect in urate reabsorption. Four offspring were moderately affected. This family represents the sixth Jewish Iraqi family with familial isolated presecretory uricosuria, and emphasizes the marked prevalence of this disease among the Iraqi Jewish population. Since the inheritance of the presecretory defect is autosomal recessive, we suggest that this family is an example of pseudodominant transmission. The combined pyrazinamide-probenecid test may cause a reduction in glomerular filtration rate and filtered load of urate and thereby affect urinary excretion rate of urate in patients with urate wasting.