The concentration of acute phase proteins following burn is known to increase in serum rapidly, while that of fibronectin often decreases. Fibronectin (Fn) has been demonstrated to serve as an opsonin involved in the ingestion phase in phagocytic process. On the other hand, some acute phase proteins such as alpha-1 acid glycoprotein (AG) may inhibit phagocytic activity. In our study, the phagocytic activity of normal granulocytes was decreased by those sera in which a high level of AG was accompanied by a fall in the Fn Level. Attempts to detect a possible link between the acute phase response and fibronectin led as to study whether fibronectin and AG may interact antagonistically on the phagocytic activity of neutrophils. For this reason we calculated the Fn/Ag coefficient. We showed that an Fn/Ag coefficient in normal sera equals more than 0.20. The higher the coefficient, the better the opsonic activity of sera. We propose here that an Fn/AG coefficient may be a useful risk factor for infections in burned patients.