The Cattle Fever Tick Eradication Program was the first parasite eradication program of veterinary importance in the United States and is considered to be one of the greatest disease eradication programs of all time. The program's utilization of pasture vacation and dipping of cattle in acaricide has been extremely successful for controlling Rhipicephalus (Boophilus) microplus (Canestrini) and R. (B.) annulatus (Say), collectively known as cattle fever ticks, on cattle along the Texas border with Mexico for decades. However, the increase of white-tailed deer, Odocoileus virginianus (Zimmermann), populations in South Texas over the last 50 yr has compromised the success of the program. R. (B.) microplus and R. (B.) annulatus infestation data have confirmed that O. virginianus can support the maintenance and movement of both species of cattle fever tick within the permanent quarantine or buffer zone in SouthTexas along the Rio Grande, and also in the cattle fever tick-free area north and east of the buffer zone. Over the last two decades, increasing populations of exotic nilgai antelope, Boselaphus tragocamelus (Pallas), in South Texas have further complicated cattle fever tick eradication efforts. Historical cattle fever tick infestation data, host source data, and geographical data support the continued role of O. virginianus in maintaining reinfestations of R. (B.) microplus and R. (B.) annulatus in South Texas as well as the increasing role of nilgai antelope in cattle fever tick maintenance and dispersal.