The effects of camostat mesilate (CM), a derivative of gabexate mesilate developed for oral use, on primary glomerulonephritis (GN) and chance hematuria and/or proteinuria were evaluated. Fourteen patients (6 males, 8 females) with a mean age of 11 years and 3 months (range 4-16 years) were enrolled. Histological and clinical diagnoses of the 14 patients were as follows: IgA nephropathy 3, non-IgA GN 2, and asymptomatic significant microscopic hematuria [more than 100 red blood cells per high-power field (x400)] with or without proteinuria 9. They were consecutively treated with oral CM (100 mg twice a day) when they were confirmed to have continuous significant microscopic hematuria and/or proteinuria after a few months of observational follow-up. Urinary findings were normalized in 10 of the 14 patients (85.7%) between 1 month 1 week and 10 months (mean 4 months) after administration of CM. Hematuria cleared in 11 of 13 patients, and proteinuria disappeared in 4 of 5 patients. The mean duration of CM administration was 21.7 +/- 9.1 months (range 4-37 months). At present, 3-12 years after discontinuation of CM therapy, their urinary findings remain normal at 9 years 10 months to 26 years 6 months of age. In conclusion, there appears to be an association between the oral use of CM and reduction in significant microscopic hematuria and/or proteinuria. Oral CM therapy could represent a practical primary care approach to chance hematuria and/or proteinuria in children.