Glutathione S-transferases (GSTs) are a family of enzymes involved in the detoxification of a wide range of chemicals including chemical carcinogens. Human cytosolic GSTs are divided into four major classes; alpha, mu, pi and theta. This study was performed to evaluate the influence of age and gender on the GST isoenzyme expression and glutathione (GSH) content in lymphocytes. Blood was collected from 124 healthy controls, which were divided into age groups of 20-40 years (21 females, 20 males), 40-60 years (20 females, 21 males) and 60-80 years (20 females, 22 males). Lymphocytes were isolated by density centrifugation on Histopaque-1077. After homogenization, cytosolic fractions were isolated. Herein, GST isoenzyme levels were determined by densitometrical analysis of western blots after immunodetection with monoclonal antibodies. Total GSH content was determined by high performance liquid chromatography after conjugation with monobromobimane. Spearman rank correlation and Wilcoxon rank sum tests were used for statistical evaluation. Lymphocytic GSTmu and pi levels were not correlated with age or gender. GSTalpha was not detectable in lymphocytes. GSH contents were not different in males and females, but decreased with age in both males and females. In age group 60-80, GSH content was significantly lower as compared with age groups 20-40 and 40-60 in both sexes. Since high GSH is an essential factor in the detoxification of many compounds, these data indicate that the detoxification potential of the GSH/GST system in lymphocytes may decrease with age in man.