One of the major problems in the use of catheters is their thrombogenicity, since the embolization of clots near the central nervous system or the coronary arteries can cause permanent damage. In this work we have compared the in vivo thrombogenicity of four different angiography catheters and their in vitro activation of fibrinogen binding and platelet retention. The thrombogenicity of catheters has been evaluated in angiographic conditions by kinetic evaluation of the reduction of blood flow rate through the catheters. The binding of adhesive proteins (fibrinogen and von Willebrand factor [vWF] was studied in vitro using a direct-ELISA technique after circulation of anticoagulated whole blood through sections of catheters. The retention of platelets was studied in vitro using 111Indium-labelled platelets. Fibrinogen binding and platelet retention both seem to be good predictors of catheter thrombogenicity, fibrinogen being the better of the two. The most thrombogenic material has the highest fibrinogen and platelet retention rate. This study also confirms the inefficiency of albumin precoating for the prevention of fibrinogen deposition. The determination of fibrinogen deposition by direct-ELISA technique and platelet retention rate is very useful for preclinical testing of catheters.