1. In 37 patients with cirrhosis of the liver of different severity (11 in class A, 18 in class B, and 8 in class C, according to Child's criteria modified by Hobbs), inulin and p -aminohippurate clearances, total fractional protein excretion and the fractional clearances of α 1 -acid glycoprotein, albumin, transferrin, α 2 -macroglobulin and β 2 -microglobulin (in 20 patients) were determined. 2. Inulin clearance was lower than 70 ml/min in 19 patients and p -aminohippurate clearance was lower than 300 ml/min in 20 patients. Total fractional protein excretion was above normal in 19 patients; α 1 -acid glycoprotein fractional clearance was above normal in 11, albumin fractional clearance in 10, transferrin fractional clearance in five, α 2 -macroglobulin fractional clearance in three, and β 2 -microglobulin fractional clearance in 10. 3. The increases in protein excretion were independent of any impairment of renal tubular function. An inverse relationship between protein excretion and the clearances of inulin and p -aminohippurate was found. No difference in protein excretion was found between the three groups of patients with different degrees of liver damage. 4. The results suggest that in cirrhosis an increase in glomerular permeability is frequent, though generally slight; it is correlated with an impairment of kidney function and is independent of the severity of the liver damage.