Rhipicephalus sanguineus, the brown dog tick, is endemic throughout the world wherever domestic dogs are present. It has been recently reported by some veterinarians in the city of Laredo, Texas, USA, that Lyme disease, the most common tick-borne disease in the Northern United States, is present in local domestic dogs. Fully engorged R. sanguineus ticks were collected and their DNA was purified. The ticks were screened to determine the prevalence of Borrelia, Rickettsia and Ehrlichiaspecies. Sequences related to Borrelia burgdorferiin 9.8% (n=11/112), “Candidatus Borrelia lonestari” in 16.9% (n=19/112) and Ehrlichia canis in 12.5% (n=14/112) were detected by PCR. Sequencing has confirmed the presence of DNA from Ehrlichia canisand “Candidatus B. lonestari”, corroborating that Borrelia and Ehrlichia are present in domestic dogs in South Texas.