Tyzzer's disease was induced in outbred, 3- to 4-week-old female Mongolian gerbils (Meriones unguiculatus) by oral inoculation of either a yolk sac preparation containing spores or a suspension of infected mouse liver. Clinical signs and lesions were similar regardless of the inoculum. Nests of Bacillus piliformis were seen in follicle associated epithelium of ileal Peyer's patches by 24 hours post-inoculation. Disease severity peaked at the fifty through seventh days. Many animals died during this time, and they had lesions in the intestinal tract, liver, and myocardium. Lesions began to resolve in animals surviving past the seventh day of infection. Because of the unique susceptibility of gerbils to Bacillus piliformis infection, they may be useful as an aid to study the natural course of Tyzzer's disease and as sentinel animals. They also may serve as a valuable diagnostic tool as the recipient of suspect material.