Urinary albumin fragments (uAF) from patients with NIDDM were analyzed as a possible factor in the early discovery of diabetic nephropathy before emergence of microalbuminuria. SDS-PAGE and immunoblot assay were employed for detection of uAF. Samples from 252 patients with NIDDM, 158 patients with non-diabetic diseases, and 48 healthy volunteers were examined; uAF were detected in 139 (55.2%), 94 (59.5%), only one (2.1%), respectively. In diabetic patients with normoalbuminuria, uAF were detected in 48 out of 159 cases (30.2%). Two years after the initial study, 3 of the 17 diabetic patients (17.6%) with normoalbuminuria and uAF showed micro- or macroalbuminuria. It was concluded that detection of uAF might be useful for the early detection of diabetic nephropathy in NIDDM.