Abstract: A multi-level, animal inhalation toxicology research chamber system is disclosed. It has an enclosed airtight chamber defining a central enclosure with vertically extending inlet and outlet plenums at its opposite ends. A plurality of vertically spaced horizontally extending perforated shelves with underlying collection pans are provided for supporting laboratory animal cages vertically spaced on a plurality of levels. Air is distributed from the inlet plenum to the outlet plenum means through the animal cages in a horizontal direction. The collection pans prevent vertical fluid communication and the perforated shelves permit passage of animal waste into the collection pan, thereby preventing animals from contacting their own waste and preventing waste from falling on animals located beneath an upper cage.