Plasma fibronectin levels, assayed by rocket immunoelectrophoresis, were measured in adult burn patients with 25-75 per cent total body surface area burns. Significant differences in the level of plasma fibronectin were detected in the one fatally injured patient prior to death (at 48 and 24 h) as a precipitous and persistent drop to 0.07 and 0.09 g/l, respectively. This deficiency coincided with early clinical signs of sepsis, the severity of which was not clinically apparent prior to overwhelming sepsis and incipient shock. This report supports previous suggestions that secondary deficiencies in plasma fibronectin may be predictive of mortality occurring after day 6 postburn. The need for routine assay of plasma fibronectin using rocket immunoelectrophoresis is demonstrated.