Dose-ranging studies with a batch of factor IX concentrate have been performed in a canine non-stasis model of thrombogenicity. Doses between 50 and 200 IU/kg were infused over a 30 min period, and beagles were found to be more sensitive than greyhounds with regard to subsequent alterations in haemostatic parameters over a 150 min period. In beagles we detected significant increases in plasma fibrin(ogen) degradation products and reduction in fibrinogen concentrations in a dose-related manner after infusion of factor DC concentrate over the range 50–150 IU/kg. Plasma fibrinopeptide A was the most sensitive marker of activation of coagulation with significantly increased levels after factor IX at 50 IU/kg compared with control infusions of albumin. Recovery of infused factor IX was similar to values reported in man. In these experiments, measurement of urinary fibrinopeptide A did not prove to be a useful indicator of thrombogenicity. In conclusion, the beagle non-stasis model will provide a sensitive method to quantify the unwanted thrombogenic activities associated with the use of high doses of certain factor IX concentrates.