Background: Major surgery is known to suppress T-cell function; however, its differential effects on the production of helper T-cell type 1 (T(H)1) and type 2 (T(H)2) cytokines remains unknown. Objective: To measure the production patterns of T(H)1 (interleukin 2 [IL-2] and interferon γ) and T(H)2 (IL-4 and IL-10) cytokines following major surgery. Design, Setting, and Patients: A cohort study of patients (both active and former members of the armed forces) at a military hospital. Intervention: Aortic surgery or carotid endarterectomy and measurement of serum IL-6 levels by enzyme-linked immunosorbent assay. Main Outcome Measures: Unstimulated and stimulated intracellular levels of IL-2, IL-4, IL-10, and interferon γ in CD4+, CD8+, and γδ+ T cells and serum IL-6 levels immediately before and for 2 days after aortic surgery or carotid endarterectomy. Results: No unstimulated production of T(H)1 or T(H)2 cytokines was detected. Stimulated intracellular levels of IL-2 and interferon γ were significantly depressed during the postoperative period in all T-cell subsets in both patient groups. There were no postoperative increases in stimulated IL-4 or IL-10 levels. Conclusion: Major surgery suppresses the potential responses of T(H)1 cytokines without enhancing production of T(H)2 cytokines.