The aim of the study was to evaluate serum α-glutathione S-transferase (s-GSTA) levels in patients with cystic fibrosis (CF) and to compare s-GSTA with other liver function tests and with a hepatic ultrasound scan (US). The cytosolic enzyme, a-glutathione S-transferase is predominantly found in the liver and is distributed uniformly in the liver tissue. In our study s-GSTA levels were measured in 37 CF patients aged 1 to 28 years (mean age 10.4 years, 24 males). The control group consisted of 27 patients aged 2 to 17 years (mean age 8.5 years, 18 males). The presence of hepatobiliary abnormalities was assessed by clinical examination, ultrasound scan, s-GSTA, and conventional liver enzymes: alanine aminotransferase (ALT), alkaline phosphatase (ALP), aspartate aminotransferase (AST) and g-glutamyl transferase (GMT). The calculated 5-95 % range of s-GSTA for the control group was 0.098-2.54 mg/l, for the CF group 0.43-9.76 mg/l. Mean s-GSTA level in the control group was 1.55 mg/l (S.D.=1.57), and 2.05 mg/l (S.D.=2.60) in the CF group. In the group of CF patients, the serum levels were significantly higher than in the control group (P<0.01). No significant correlation existed in the CF group between s-GSTA and conventional liver tests (ALT, AST, ALP and GMT). Four patients in the CF group had hepatobiliary abnormalities detectable by conventional liver tests, s-GSTA and US. Four patients had abnormal s-GSTA, while conventional liver tests and US were normal. One other patient had abnormal hepatic US, but normal standard liver tests and s-GSTA. The study has suggested that a raised s-GSTA level might be a marker of possible pathological changes of the hepatobiliar system in CF patients. Serum GSTA seems to be a more sensitive marker than transaminases for the monitoring of hepatocellular integrity and as an early predictor of hepatic damage., K. Šídlová, V. Skalická, K. Kotaška, M. Pechová, M. Chada, J. Bartošová , Z. Hříbal, J. Nevoral, V. Vávrová, R. Průša., and Obsahuje bibliografii