Cilnidipine, an L-/N-type calcium channel blocker, dilates the efferent glomerular arterioles in an experimental model and shows a renoprotective effect, but its clinical benefits and safety have not yet been assessed in type II diabetics with albuminuria. The objective of this trial was to evaluate the effect of reducing albuminuria in type II diabetic patients with a combination therapy consisting of valsartan plus cilnidipine versus monotherapy with valsartan. An open-label, randomized controlled trial was conducted from April 2002 to October 2003 in 87 Japanese patients aged 31-90 years with type II diabetes showing albuminuria (urinary albumin/creatinine ratio: 10-300 mg/g). The patients were randomized to receive either valsartan (n=41) or valsartan plus cilnidipine (n=46) once daily for 1 year. The primary end point was the percent change in the albumin/creatinine ratio. The secondary end points were the progression/regression of albuminuria, blood pressure (BP), renal function, and safety. After 1 year, the albumin/creatinine ratio was found to have decreased more markedly in the valsartan plus cilnidipine group than in the valsartan group (reduction rate -44+/-11% (s.e.) versus -9+/-7% (s.e.); P=0.014 by analysis of covariance). Although a significant reduction was observed in the systolic and diastolic BP of both groups from baseline to 1 year (P<0.0001, respectively), there was no significant difference in the change in the BP between the two groups (systolic BP, P=0.066; diastolic BP, P=0.391). There were also no significant differences in the side effects between the two groups. Cilnidipine was thus found to show an additive effect with valsartan and thereby caused a reduction in albuminuria in type II diabetics.