Plasma fibronectin time course was studied in 30 patients versus clinical criteria: body surface area burn (BSA), unit burn standard (UBS), and infection state. The mean value for all the population was lowest within days 1-3. No correlation was observed between fibronectin concentration and clinical criteria, either at admission or subsequently. Fibronectin levels of nonseptic patients (Group 1) did not differ significantly during the first days from those of patients who, at any time of their hospitalization, would become moderately infected (Group 2) or septic (Group 3). Afterwards, protein concentration of Group 1 increased regularly and hyperopsonization was observed from day 17 until the end of the study, day 35. In contrast, protein levels of Groups 2 and 3 remained low with a further improvement for moderately infected patients. A marked and significant difference was observed between nonseptic patients and septic patients, from the 6th postburn day. Variation of Groups 2 and 3 may be related to the infectious period, whatever the BSA or UBS index evolution. Since infection was related to low fibronectin level in the three deaths observed, it appears that opsonic protein cryoprecipitate would be of value in the treatment of burn victims.