Correlative interconnections between plasminogen activator (PA) activity (fibrin plate method) and level of urokinase antigen (Ag UAP) and tissue PA antigen (Ag TAP) in urine and blood (ELISA) were studied in 60 patients with chronic glomerulonephritis (CGN) and 38 patients with amyloidosis. The high degree of positive correlation between blood and urine initial PA activity and Ag UAP content was found. This suggests the possible leading role of UAP in formation of the basal fluctuations of fibrinolytic activity in blood and urine. High degree of correlation--r = +0.84 and p < 0.001--was found between blood Ag UAP and urine Ag TAP in amyloidosis only. The functional protein loading probe revealed great importance of high urine and blood AP activity in realizing of ultrafiltration renal process--in CGN and amyloidosis.