Transvascular escape rates of albumin and immunoglobulin-G, IgG (TERalb and TERIgG, i.e, the fractions of intravascular mass of albumin and IgG passing to the extravascular space per unit time) were determined simultaneously from the disappearance of intravenously injected 131I-labelled human serum albumin and 125I-labelled human IgG in eight patients with cirrhosis of the liver. The mean wedged hepatic venous pressure was 22 mmHg (range 13-34). TERalb and and TERIgG/TERalb ratio was on average 8.4 +/- 0.8%/h (SD), and 7.4 +/- 1.9%/h (SD), respectively and these values are significantly increased compared to normal subjects [TERalb = 5.2 +/- 1.0 %/h (SD) and TERIgG = 3.0 +/- 0.7 %/h (SD), P less than 0.001]. The TERIgG/TERalb ratio was on average 0.88 +/- 0.20 (SD), which is significantly higher than that of normals [0.58 +/- 0.08 (SD), P less than 0.005]. The results indicated that increased filtration (bulk flow) is the dominant process of the increase microvascular protein escape in cirrhosis, due most likely to increased hepatic, but also to increased extrahepatic splanchnic transcapillary protein flux.