The course of in vivo pathogenicity of Yersinia pseudotuberculosis in groups of rabbits and gunnea pigs were examined. One group of the animals was infected orally with 108 cfu/ml of test organism and the second group with standard reference strains. The third group was dosed with clean water as negative control. Both controls and Y. pseudotuberculosis infected animals were closely monitored for clinical signs for three weeks during which loss of body weight, rise in temperature, ruffling of fur were noticed. Pure isolates of the organisms were re-isolated from the faecal samples of the infected rabbits and guinea pigs. Animals orally fed with clean water showed no symptoms of yersiniosis. Rabbits infected with Y. pseudotuberculosis showed signs of illness while guinea pigs did not show any clinical sign. Visceral organs of infected rabbits showed enteritis with necrotic lesions but no pathological changes were observed in all guinea pigs including the controls. In the clinically ill animals, tissues analyzed demonstrated polarized profile and inflammatory cell influx throughout the course of the test. These findings should assist the Veterinary Pathologist recognize suspected cases of enteritis due to Y. psuedotuberculosis in the field among similar animal species.