Decline of kidney function with time and its influencing factors were investigated in the present longitudinal study in Type 2 (non-insulin-dependent) diabetic patients with clinical diabetic nephropathy. Compared to a control group of Type 2 diabetic patients without proteinuria, the proteinuric patients showed a higher prevalence of hypertension, higher systolic blood pressure values and serum triglyceride levels. The annual loss of glomerular kidney function was much higher in the proteinuric patients (5.3 ml.min-1 x 1.73 m2) than in the control subjects (0.9 ml.min-1 x 1.73 m2). Correlation analyses revealed a close correlation between the annual decrease of kidney function and the factors, systolic and diastolic blood pressure, triglyceride and postprandial blood glucose level as well as body mass index. Regression analyses showed for the first time that in addition to the systolic blood pressure and metabolic control, the triglyceride level is also an independent factor influencing the progression of nephropathy. Higher values of these parameters were associated with a more rapid deterioration of kidney function.