A positive family history of coronary heart disease (CHD) is one of the most predictive risk factors of CHD. Many children with increased risk of CHD because of their positive family history of CHD do not present other risk factors, such as altered serum lipid profile. Oxidative stress plays an important part in the pathogenesis of atherosclerosis. Serum antioxidants and intracellular enzymatic antioxidants composed mainly of glutathione peroxidase (GSH-Px), catalase (CAT), superoxide dismutase (SOD) and glutathione reductase counterbalance oxidative stress. Diminished activity of this system may lead to accelerated progression of atherosclerosis. The aim of this study was to assess the activity of CAT, GSH-Px, SOD and glutathione reductase in children with a family history of premature CHD who did not present any other major risk factors of CHD (diabetes, obesity, dyslipidaemia or hypertension). Twenty-two healthy children from high-risk families, selected according to the National Cholesterol Education Program definition, were enrolled in the study. The control group comprised 18 children without a family history of CHD. All the children were healthy and had been screened for hyperlipidaemia, diabetes, hypertension and obesity prior to the study. The erythrocyte activity of CAT, GSH-Px, SOD and glutathione reductase was assessed. Children at high risk of CHD had a statistically significant lower level of GSH-Px and CAT activity than the children in the control group. There were no statistically significant differences in the activity of SOD and glutathione reductase.