Fibronectin is a large, adhesive glycoprotein, also called opsonic α 2 surface-binding glycoprotein. This glycoprotein which participates in all adhesions may modulate wound healing; plasma fibronectin, because it is opsonically active, may mediate reticulo-endothelial activity. Citrated plasma samples were analysed from twenty surgical patients with digestive cancer. The samples were obtained preoperatively and on 1st, 3rd, 7th, 14th and 28th postoperative days. Fibronectin assay was made by laser immunonephelometry. Other samples were obtained from a population of 340 healthy male and female subjects whose age ranged from 10 to 70 years, so that reference could be made to the standard mean of fibronectin related to the age of each patient. In the surgical patients, there was a significant decrease in fibronectin from the first to the third postoperative day. On the 7th day, there was a secondary increase of fibronectin levels which exceeded the preoperative values at the 14th and 28th days. There was no plasma dilution when the samples were collected, this being shown by protidaemia, osmolarity and haematocrit which were measured at the same time. « Septicand « non septicpatients were compared. For septic patients, fibronectin levels were lower and the secondary increase occurred later than in the non septic patients. Patients with no secondary increase did not recover and died. Fibronectin levels were compared with other classical parameters of nutritional assessment, i.e. albumin, prealbumin, transferrin and urinary creatinine indexes. These parameters were not well correlated. However, this study may indicate the usefulness of fibronectin as an indicator of nutritional status and of non specific host defence.