The gene encoding human coagulation Factor V (FV), one of the cofactors in the blood clotting process, has been mapped to chromosome 1 by both Southern hybridization to DNA from human-hamster somatic cell hybrids and in situ hybridization. The whole plasmid pUC3A containing a 1.5-kb cDNA sequence for FV was P-32-labeled for Southern analysis and H-3-labeled for in situ hybridization to metaphase chromosomes. The results localized the FV gene to the region of 1q21-25. (C) 1988 Academic Press, Inc.