To evaluate the clinical effect of ibudilast, a prostacyclin-mediated vasodilator and antiplatelet agent, on diabetic nephropathy, 8 nonhypertensive patients with type 2 diabetes mellitus (DM; 4 men and 4 women, mean age: 58.9 +/- 11.4 years, duration of diabetes: 16.9 +/- 3.2 years) with microalbuminuria [20-200 mg/g creatinine (Cr)] were administered ibudilast (30 mg/day) for 18 months (ibudilast group). The urinary albumin excretion index (UAE, mg albumin/g Cr) was compared with 8 age-matched type 2 DM with microalbuminuria (control group). During the study, the UAE significantly decreased in the ibudilast group, while it significantly increased in the control group. After 18 months, the UAE (52 +/- 19 mg/g Cr) in the ibudilast group was significantly (p < 0.05) lower than that (99 +/- 46 mg/g Cr) in the control group. These results suggest that ibudilast may inhibit the progression of early diabetic nephropathy in type 2 DM.