The present study was conducted on 8 patients with advanced diabetic nephropathy who showed a significant reduction of proteinuria through ACE inhibition. Camostat mesilate, one of the most potent protease inhibitors developed for oral use, was administered to these patients at a daily dose of 600 mg starting after 4 weeks of ACE inhibitor administration. Laboratory data were obtained 1) just before the ACE inhibition, 2) after 4 weeks of the ACE inhibitor single treatment, and 3) after another 4 weeks of the additional treatment with camostat mesilate. The urinary protein excretion decreased from 1) 10.1 +/- 1.3 to 2) 7.3 +/- 1.1, and 3) 4.6 +/- 0.9 g/day [mean +/- SEM; significance of difference 1)-2), p less than 0.05; 2)-3), p less than 0.01], and the serum total protein values increased from 1) 5.0 +/- 0.3 to 2) 5.2 +/- 0.2, and 3) 5.4 +/- 0.3 g/dl [1)-3), p less than 0.05]. The plasma levels of fibrinogen, and of E fragment and D-dimer of FDP changed from 1) 476 +/- 43 to 2) 477 +/- 41, and 3) 374 +/- 33 mg/dl [2)-3), p less than 0.01], from 1) 125 +/- 19 to 2) 147 +/- 27, and 3) 104 +/- 30 ng/ml [2)-3), p less than 0.05], and from 1) 261 +/- 60 to 2) 272 +/- 86, and 3) 185 +/- 56 ng/ml [2)-3), p less than 0.05], respectively.(ABSTRACT TRUNCATED AT 250 WORDS)