Pathomorphological picture and agents of spontaneous Yersinia infection in monkeys are described. The infection was characterized by polymorphic and generalized changes (usually inY. pseudotuberculosis infection) or mainly local changes involving the intestine and asymptomatic carriership (inY. enterocolitica infection). Of 8 monkey species, red monkeys were the most sensitive to Yersinia. Similarity of human and simian yersiniases allows to use monkeys as the experimental model for studies of this pathology.