Plasma albumin leaks into urine as a result of glomerular hypertension and basement membrane injury, while urinary type IV collagen derives from mesangial matrix and glomerular basement membrane. The purpose of this study was to elucidate the pathophysiological significance of these urinary microproteins as an indicator of cardiovascular organ injuries in hypertension. In health-checkup participants without diabetes, proteinuria, or microhematuria, and who were not being treated for hypertension or any other disease at the time of enrollment, urinary albumin and type IV collagen were measured and their relations to organ injuries and cardiovascular risk factors were evaluated. Of 1,079 subjects (40-to 65-year-old; 256 men and 823 women) enrolled in the study, 120 (11.1%) had untreated hypertension exceeding 140190 mmHg. Urinary albumin was positively correlated with both age (r= 0.16, p< 0.001) and systolic blood pressure (r= 0.27, p< 0.001). Urinary type IV collagen was not only positively correlated with age (r= 0.12, p< 0.001) and diastolic blood pressure (r= 0.14, p< 0.001) but also negatively correlated with blood hemoglobin (r=-0.12, p< 0.001). Urinary albumin, but not type IV collagen, had a significant relation to electrocardiographic signs of left ventricular hypertrophy (p= 0.012) and retinal arteriosclerosis on fundoscopy (p< 0.001). Thus both albumin and type IV collagen would seem to have increased in association with age and hypertension in this cohort. It is suggested that urinary albumin is an indicator not only of renal injury, but also possibly of development of cardiac hypertrophy and arteriosclerotic changes. Urinary type IV collagen, on the other hand, may be associated with renal tissue injuries that affect erythrokinetics.(Hypertens Res 2000; 23: 459-466)