In 1993, 80 patients (43 female and 37 male) with tick-borne encephalitis were hospitalized in Clinic of Neuroinfections and Parasitic Diseases of Medical School in Białystok. 6 (7.5%) patients were jaundiced, 16 (20%) had hepatomegaly. We noticed increased enzymatic activity of aspartate aminotransferase (x = 74.5 U/l) in 9 (11.25%) cases, alanine aminotransferase (x = 89.5 U/l) in 11 (13.75%) cases, increased level of bilirubin in blood (from 1.4 to 3.5 mg/dl) in 7 (8.75%) cases. Protein level in blood was average x = 5.95 g/dl, percentage of albumin was average x = 48.61%, globulin--x = 14.62%. Prothrombin index and ammonia blood level were in normal range. Observed pathological changes were transient and referred mainly to patients with severe clinical course of disease.