Eighty patients with yersiniosis (40 with intestinal yersiniosis, 40 with pseudotuberculosis) were examined for clinical and allergic characteristics (collection of allergological histories, identification of the most common allergic symptoms of the disease and determination of the index of mast cell degranulation). According to the data obtained, the patients with yersiniosis are admitted to the hospital with an aggravated premorbid condition in the form of body allergization, in whose origin both hereditary and acquired factors are of importance. The allergic manifestations of the disease are more pronounced in patients with pseudotuberculosis. In the acute disease period, noticeable allergization of the sick body develops whatever the gravity of the disease in both infections whereas during convalescence, only in patients with the recurrent infectious process.