Cotton aphid (Aphis gossypii G.) populations in the field have fluctuated over the past years, yet it is unknown whether infestation by these insects alters cotton (Gossypium hirsutum L.) physiology. Although it is important to determine if aphids contribute to plant stress, there is only limited information on plant stress responses after aphid herbivory. In an attempt to quantify plant stress, the activity of cotton foliar antioxidant enzymes after aphid feeding was examined. Cotton aphids were collected from cotton fields at Lonoke, AR, and reared in the laboratory. Fifty aphids were transferred to cotton (G. hirsutum 'Stoneville 474') leaves of the same age and size, and were allowed to increase in numbers without restriction. Leaf samples were collected for protein extraction and antioxidant enzyme assays after 6 d and 9 d of aphid exposure. Enzyme activities of catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), and glutathione reductase (GR) were measured. The initial population of 50 aphids increased to 137 aphids per leaf after 6 d. Of the antioxidant enzymes tested, only GR activity increased in aphid-infested leaves. After day 9 of infestation, there were 255 aphids per leaf, but the activity of foliar antioxidant enzymes was not different from control plants. In general, antioxidant enzyme activity in cotton plants was not altered by the levels of infestation and feeding duration used in this study.