Frequency of interspecific hybridization between mule deer and white-tailed deer was investigated using ribosomal DNA and nucleotide sequences from the mitochondrial cytochrome b gene. Two of 15 individuals (collected by hunters) from northwestern Texas (Kent County) were identified as hybrids based on the ribosomal DNA marker. Sequence data from the cytochrome b gene indicated that 1 individual was the result of mating between a mule deer doe and a white-tailed deer buck, whereas the second individual resulted from mating between a white-tailed deer doe and a mule deer buck. These results indicate that hybridization between mule deer and white-tailed deer is not restricted to the Trans-Pecos region of Texas. Given the low levels of genetic divergence and frequency of hybridization, the validity of recognizing mule deer and white-tailed deer as distinct species is discussed. It is concluded that without the morphological and behavioral differences these 2 taxa could be considered subspecies rather than distinct species.