We determine the concentration of proapolipoprotein (proapo) A-I and its ratio with total apolipoprotein (apo) A-I (proapo A-I/total apo A-I) in plasma of patients with liver disease; we used a noncompetitive sandwich method, an enzyme-linked immunosorbent assay. The mean (SD) proapo A-I concentrations in patients with decompensated or compensated liver cirrhosis were higher than in normal subjects: 88 (25), 105 (36), and 69 (25) mg/L, respectively. The mean (SD) ratio (expressed as %) for each of these types of liver cirrhosis was also higher than in normal subjects: 10.0 (3.5), 10.2 (3.9), and 4.6 (1.6), respectively. In the patients, the proapo A-I concentration was positively correlated with the concentration of high-density lipoprotein subtype 2 cholesterol (HDL2-C) (r = 0.736), and the proapo A-I/total apo A-I ratio was correlated inversely with the HDL3-C concentration (r = -0.609). The activity of proapo A-I converting enzyme in patients with liver cirrhosis (62 +/- 30 nmol/h per liter) was significantly (P < 0.01) lower than that in normal subjects (172 +/- 55 nmol/h per liter). The increases of the plasma proapo A-I concentration and ratio in patients with liver cirrhosis may be caused by a decreased production of the converting enzyme in the liver. The increase of plasma proapo A-I may thus also affect the circulating HDL subtypes.