We measured urinary albumin (U-Alb) and type IV collagen (uIV.C) in spot urine collected from 82 patients with non-insulin-dependent diabetes mellitus (NIDDM) and 205 controls. Eighty-two NIDDM patients that had no increased excretion of either U-Alb or uIV.C were observed for 6 months. Prevalence of increased excretion of U-Alb and uIV.C at 6 months in these patients were 32.9%, and 62.2%, respectively. Increased excretion of uIV.C was detected in 27 patients without microalbuminuria. chi(2) analysis suggested that uIV.C was more sensitive than U-Alb, and that hypertension enhanced increased excretion of both U-Alb and uIV.C. uIV.C was significantly correlated (P<0.01) with U-Alb but not glycosylated hemoglobin A1C (HbA1C) in NIDDM patients. Taken together, uIV.C may be a useful marker for early diabetic nephropathy.