 Microalbuminuria in diabetic patients is an established risk marker for the progression of diabetic nephropathy and for cardiovascular mortality. Intervention trials have demonstrated that drugs that blockade the renin-angiotensin system can reduce microalbuminuria in Caucasian patients with type 2 diabetes mellitus and microalbuminuria, regardless of blood pressure level. However, it remains uncertain whether angiotensin receptor blockers or calcium channel blockers give a greater reduction of microalbuminuria. The Shiga Microalbuminuria Reduction Trial SMART is a prospective, multicentre, randomized, active-controlled, two-arm parallel treatment group comparison study aimed at evaluating reduction of microalbuminuria in 160 Japanese hypertensive patients with type 2 diabetes mellitus and microalbuminuria. The trial consists of an 8-week observation period for screening and washout, and a 24-week intervention period. After the observation period, patients are randomized to either amlodipine 5 mg once daily or valsartan 80 mg once daily as an initial dose. After four weeks, if patients cannot achieve the target blood pressure 13080 mmHg with the initial dose of a study drug, doses are titrated up to amlodipine 10 mg once daily or valsartan 160 mg once daily. The primary endpoints are a change in the rate of urinary albumin excretion from baseline, a normalization of microalbuminuria, and a 50 reduction in urinary albumin excretion from baseline, which are compared between treatment groups. This study will provide additional data for the treatment of hypertension and microalbuminuria and has important health care implications for Japanese patients with type 2 diabetes. 