We report on our laboratory and clinical experience with a new hemostatic agent made of collagen fibers and existing in the form of a loose or compressed fleece. This material was tested in two independent bleeding models on eight dogs and 21 patients. Partially compressed collagen fleece showed significantly higher hemostatic effectiveness when compared to loose fleece. This was demonstrated by gravimetric determinations of blood loss in dogs with split-thickness skin excisions and by measuring the blood loss and time of bleeding after an excision 0.5 cm deep and 4 cm wide of the edge of the spleen. The handling of partially compressed hemostatic fleece was found superior to loose or fully compressed fleece. Clinical cases included patients with liver lacerations and retroperitoneal bleeding. Collagen fleece, partially compressed, proved to be an effective topical hemostatic agent when applied directly with pressure to a bleeding surface and when folded and sutured against a bleeding surface. Postoperative injection rate was not increased nor was foreign body reaction demonstrated. The material was extremely easy to apply, did not adhere to gloves or instruments, and could be cut or molded to any desired shape.