Tissue factor, or coagulation factor III, is a membrane-bound glycoprotein and acts as a cofactor for factor VII-dependent initiation of blood coagulation. The tissue factor gene (F3) was previously assigned to human chromosome 1, region p21-pter. The present report has further refined the mapping position to 1p21-p22 using a cDNA probe for the tissue factor gene and in situ hybridization to metaphase chromosomes.