The coagulation cascade is controlled by several anticoagulant safeguards that avoid excessive clot formation. Disorders of these anticoagulant mechanisms are an important health problem, as they lead to increased risk of thromboembolism. Protein C deficiency is probably the most extensively studied abnormality in natural anticoagulants. Under the auspices of the Subcommittee on Plasma Coagulation Inhibitors of the Scientific and Standardization Committee of the International Society of Thrombosis and Haemostasis a working party of researchers maintains a database of mutations that have been characterized in the protein C gene. The 1995 update of this database comprises 331 entries that describe 160 unique mutational events. Here essential features of the database are reviewed.