The effect of the angiotensin II receptor blocker, candesartan cilexetil, on proteinuria was examined in a prospective, multicenter, randomized, double-blind study in Japanese subjects with type 2 diabetes. This study enrolled diabetic subjects with confirmed proteinuria into four groups for 12 weeks of treatment with placebo or candesartan cilexetil 2, 4, or 8 mg. The contribution of the angiotensin converting enzyme (ACE) gene polymorphism to the effect of candesartan cilexetil was also examined. In 127 subjects, candesartan cilexetil showed a dose-related reduction in proteinuria after 12 weeks of treatment (F = 9.45, P = 0.0013), with a 18.1% reduction in the 4-mg group, and a 5.8% reduction in the 8-mg group, in contrast to a 32.2% increase in the placebo group, and a 0.8% increase in the 2-mg group. These results indicate that candesartan cilexetil is useful in reducing proteinuria in diabetic subjects when compared with placebo. In addition, candesartan cilexetil seems to be effective in subjects with both the II and DD genotypes of the ACE gene.