The gerbil or jird (Meriones unguiculatus) has been reported to be an excellent host for the ruminant nematodes Trichostrongylus axei and T. colubriformis (Leland, 1963, J. Parasitol. 49: 617-622; Kates and Thompson, 1967, Proc. Helminthol. Soc. Wash. 34: 228236; 1968, Ibid. 35: 102-106). These nematodes are found in the abomasum and small intestine, respectively, of the ovine and bovine hosts. This study was undertaken to determine if a similar segregation occurred in the gastrointestinal tract of the gerbil. In the first study, each of five gerbils was inoculated with 1,000 T. colubriformis larvae of calf origin. Twenty-eight days after infection, the animals were killed. The stomach and small intestine were removed from each animal and opened longitudinally. After soaking in physiological saline for 2 hr, the organs and their contents were preserved with 10% formalin. Total counts and identification of all worms recovered from stomach and small intestine were made. Results are summarized in Table I. All the T. colubriformis were found in the small intestines. Another study was conducted, using T. axei of sheep origin as the inoculum. The experimental format was identical to the previous study. Results are summarized in Table I. The T. axei were found in stomachs of each gerbil examined. Those found in the small intestine were judged to have moved there during the necropsy procedure. In a third study, three groups of five gerbils each were inoculated with 10,000, 3,000, or 1,000 infective larvae of a mixed culture obtained from a lamb known to be infected with Trichostrongylus spp. and other worms (Cooperia, Haemonchus, and Ostertagia). Twenty-eight days after infection, the gerbils were killed and processed as in previous studies. More than 99% of the total T. colubriformis recovered were found in the small intestine at each infection level. Similarly, 99% of the total T. axei recovered were found in the stomach at each infection level. Five T. vitrinus were recovered, four from the small intestine of one gerbil and one from the stomach of another gerbil. None of the other species of worms was recovered. We conclude from these studies that adult T. axei will localize almost exclusively in the gerbil stomach, whereas adult T. colubriformis will localize exclusively in the gerbil small intestine. This is the first report of the gerbil as an experimental host for T. vitrinus.