A prospective study was made of 38 adult patients (15 male and 23 female, age 30.5 +/- 10.8 years) with isolated hematuria of unknown etiology in which presence of hypercalciuria and/or hyperuricosuria without lithiasis was observed. Eighteen patients also referred episodes of macroscopic hematuria. Twenty-six patients had hypercalciuria (5.1 +/- 1.4 mg/kg/day), 29 hyperuricosuria (1053 +/- 198 mg/day) and 17 presented both alterations. A four months treatment was instituted with thiazides in patients with hypercalciuria and allopurinol in those with hyperuricosuria. From the first months and throughout the whole therapy, urinary excretion of calcium an uric acid became normalized in all cases. In 22 patients (57.8%) (Group I: Respondents) hematuria disappeared coinciding with normalization of calcium and uric acid values in urine and was maintained during the follow-up months. In the remaining 16 patients (Group II: Non-Respondents) the hematuria condition persisted in spite of such normalization, in most cases other causes for hematuria becoming clear later. No differences with regard to age, relationship male/female nor basal calciuria and uricosuria values were seen between both Groups. Group I had a greater incidence of macroscopic hematuria episodes (64% vs 12% in Group II, p less than 0.01) and of family nephrolithiasis (64 vs 25% in Group II, p less than 0.05). We conclude that hypercalciuria and hyperuticosuria are potentially reversible causes of hematuria in adults. Therefore, urinary determination of calcium and uric acid should be included in urinary evaluation of patients with hematuria even though they do not present renal lithiasis.