Using essential knowledge and techniques familiar to Molecular Biology, it has arrived the moment to revisit old factors such as fibrinogen. An evaluation is made upon its assumed leading role as a general thrombotic risk factors and particularly of coronary heart disease event and seriousness. The fibrinogen basic relations, the genetic determination rules of its structure and the place and power of its synthesis are beared in mind. Stress is laid upon the important practical relationship between fibrinogen plasmatic concentration increase and restriction fragment length polymorphisms of beta chain promoter region event.