Two genetic lineages of the hispid cotton rat, Sigmodon hispidus, form an area of contact at one location in eastern Texas, with hybridization occurring, but the position of the contact zone in other areas of the United States remains unknown. The purpose of our study was to identify the location of the contact zone at its southernmost point. We employed a nuclear DNA fingerprinting technique, amplified fragment length polymorphism (AFLP), using 20 specimens collected from Orange, Brazoria, and Matagorda counties, Texas, along with reference specimens representative of the two lineages. Our results showed that in southeastern Texas the contact zone occurred in the vicinity of Galveston Bay.