BACKGROUND: Oxidative stress, mediated by an imbalance between oxidants and antioxidants, contributes significantly to the pathogenesis of asthma.OBJECTIVE: To evaluate the impact of serum total antioxidant capacity (TAC) on the pulmonary function of Korean asthma patients.METHOD: A total of 104 adult asthma patients enrolled from the COREA (Cohort for Reality and Evolution of Adult Asthma in Korea) programme participated in the study. Baseline clinical parameters at enrolment, and the results of pulmonary function tests at baseline and 1 and 2 years after enrolment were collected. TAC at baseline was measured using a Trolox-equivalent antioxidant capacity assay. Patients were divided into two groups based on TAC levels, and various clinical parameters were compared.RESULT: Serum TAC levels correlated with forced expiratory volume in 1 second (FEV1) at baseline (r = 0.22, P = 0.03). The group with higher baseline TAC levels maintained greater mean FEV1 both 1 and 2 years after enrolment, even after adjusting for sex, age, height, weight, body mass index and smoking status.CONCLUSION: These results suggest an important link between serum TAC levels and pulmonary function, indicating that higher TAC levels may be a biomarker for favourable prognosis in asthma patients.