In 37 patients with chronic active hepatitis, in 14 with chronic persistent hepatitis and in 11 with normal histological pattern of the liver the serum activity of N-acetyl-beta-glucosaminidase and the 24-hour excretion of hydroxyproline with urine were determined. The 24-hour excretion of hydroxyproline was similar in all groups of patients, while the activity hepatitis and higher than in those of chronic persistent hepatitis (36.9 +/- 12.9 i.u. per 100 ml versus 22.4 +/- 8.2 i.u. per 100 ml, p less than 0.05). In patients with high serum NAGL activity cirrhosis developed significantly more frequently.