A novel inhalation challenge set for the study of experimental allergic alveolitis (hypersensitivity pneumonitis) in mice was designed. A finely dispersed aerosol of allergenic extract generated by the commercial ultrasonic nebulizer TAJFUN MU1 (produced by Medbryt, Warsaw, Poland) was transported to the airtight inhalation chamber. In the chamber were placed 15 perforated containers made of transparent plastic, each containing one mouse. They were coupled in 3 units, each consisted of 5 containers. The constant flow of aerosol through the chamber was assured by commercial vacuum pump PL 2/3 (AGA LABOR S.C., Warsaw, Poland). The applied set enabled the natural exposure of mice via the inhalation route to known quantities of allergen (usually microbial) suspended in saline, and then dispersed in form of fine aerosol by ultrasonic nebulizer. This method assures the penetration of allergen into the deep parts of lungs, alveoli and bronchioli. The detailed study of histopathological and biochemical changes in the lungs of exposed animals will be the subject of further publications. So far, the retention of endotoxin in the lungs of mice exposed to the extract of a Gram-negative bacterium Pantoea agglomerans and appearance of positive serologic reactions to this extract indicate the effectiveness of the method.