Spodoptera frugiperda Sf-9 (Sf-9) and Trichoplusia ni BTI-Tn-5B1-4 (Tn-5B1-4) insect cell lines were found to contain unique assemblages of antioxidant enzymes. Specifically, the Sf-9 insect cell line contained Manganese and Copper-Zinc superoxide dismutase (MnSOD and CuZnSOD) for reducing the superoxide radical (O(2)(*-)) to hydrogen peroxide (H(2)O(2)) and ascorbate peroxidase (APOX) for reducing the resulting H(2)O(2) to H(2)O. Approximately one third of the total SOD activity was found to be MnSOD. The Tn-5B1-4 cells were also found to contain MnSOD (approximately two thirds of the total SOD activity), CuZnSOD and APOX activities. However, the Tn-5B1-4 cell line, in contrast to the Sf-9 cell line, contained catalase (CAT) activity for reducing H(2)O(2) to H(2)O. Both the Sf-9 and Tn-5B1-4 cell lines contained glutathione reductase and dehydroascorbic acid reductase activities for regenerating the reduced forms of glutathione and ascorbic acid, respectively. In addition, both cell lines contained glutathione S-transferase peroxidase activity towards hydroperoxides other than H(2)O(2). Finally, neither cell line contains the glutathione peroxidase activity that is ubiquitous in mammalian cells.