The urinary excretion of alpha-1-micro-albumin (alpha 1m) and complement components (CCs) was evaluated in the urine of 49 patients suffering from chronic glomerulonephritis (GN). Nephrotic syndrome (NS) was shown in 18 cases and increased serum creatinine level (Pcr: 115.0-159.1 mumol/l) in 9 patients. The most frequent CCs presence and the highest values of alpha 1m excretion were found in patients with membranous GN. In the early phase of the disease the alpha 1m urinary excretion was higher in subjects with NS than in those not showing the feature of it, independently of the morphological basis of the disease. Also CCs were detected mainly in the nephrotic patients. As the glomerular filtration improved a significant decrease in the urinary alpha 1m excretion was observed. The application of steroid immunosuppressive therapy resulted in the decrease of alpha 1m as well as CCs excretion. The results seem to point out that the increased alpha 1m and CCs excretion may be secondary to the activity of glomerular alternations as well as to the disturbances in glomerular blood flow.