Acetylsalicylic acid and phenylbutazone increased the bleeding significantly from standardized wounds in dogs defibrinogenated with Defibrase. Administration of dipyridamole and Xylocain® had no effect. The results were the same in dogs treated with warfarin sodium. The results demonstrate the value of using laboratory animals with an induced coagulopathy when establishing the effect on the haemostasis exerted by drugs known in vitro to interfere with platelet functions. Acetylsalicylic acid and dipyridamole did not alter the activity of the K-vitamin-dependent coagulation factors, factors V, VIII, platelet count or fibrinogen concentration