BACKGROUND. The purpose of this cross-sectional study was to investigate whether the presence of serum complement antibodies was associated with reduced one-second forced expiratory volume (FEV1) in adults. METHODS. From a stratified random sample of 18-73 year old adults, we performed measurements of serum complement fixing virus antibodies against influenza type A and B, parainfluenza type 1, 2, and 3, respiratory syncytial virus and adenovirus on 82% (n = 1239). RESULTS. In the crude data, subjects having five of the seven virus antibodies had significantly lower lung function, given as sex-, age- and height-standardized residuals of FEV1 (SFEV1), compared with those without. After adjusting in addition for smoking habits, lifetime smoking consumption and season, the lung function levels were significantly lower in subjects with influenza type B and respiratory syncytial virus antibodies compared to those without (P