Background We investigated if blood Cu++/Zn++ superoxide dismutase, glutathione peroxidase, and catalase activities are increased and total plasma antioxidant concentration is decreased in coke oven workers exposed to polycyclic aromatic hydrocarbons. Methods Ninety‐six coke oven workers participated in the study. Nonexposed workers (n = 105) were randomly sampled among power plant workers in the same age range. The examination included a questionnaire on health status, occupational history, smoking, and dietary habits. Blood samples completed the examination. Coke oven workers were classified into low‐, middle‐, and high‐exposure groups based on the benzo[a]pyrene (B[a]P) air concentrations and were further classified into the categories “topside” and “non‐topside,” according to their proximity to the ovens. Results Erythrocyte glutathione peroxidase activity increased with age (r = 0.18, P = 0.061) in power plant workers, whereas plasma glutathione peroxidase activity decreased with age (r = −0.18, P = 0.068) and erythrocyte glutathione peroxidase activity was inversely correlated with the number of cigarettes per day (r = −0.28, P = 0.08) in coke oven workers. Comparison of blood antioxidant enzyme activities and total plasma antioxidant concentration between coke oven and power plant workers showed that erythrocyte glutathione peroxidase activity was significantly lower in coke oven workers, even after adjustment for potential confounding factors. No differences were found either in other blood antioxidant enzyme activities or in total plasma antioxidant concentration between coke oven and power plant workers. Moreover, no trends toward decreased glutathione peroxidase activity among the three subgroups of B[a]P exposure were observed, and no differences either in blood antioxidant enzyme activities or in total plasma antioxidant concentration between the two groups of job categories were found. Conclusions Production of reactive oxygen species seems not to be increased in coke oven workers. Am. J. Ind. Med. 34:272–279, 1998. © 1998 Wiley‐Liss, Inc.