Two markers of fibrin formation, fibrinopeptide A (FpA) and soluble fibrin (SF), were studied in order to elucidate whether they reflected intravascular fibrin formation in the same manner. Plasma was collected for measurements of FpA and SF in 34 patients during the course of colorectal surgery. Although both parametres reflected haemostatic activation postoperatively, covariation was neither observed preoperatively, nor on the second, third, and eighth postoperative days. At 3 months following surgery, however, FpA and SF was correlated. At that time, the activation of the coagulation system has ceased. The present results demonstrate a lack of correlation between these markers of fibrin formation during clotting activation. Quite different properties of the FpA and the SF molecules, different clearance rates and distribution volumes may explain the lack of correlation observed.