Abstract: An inhalation apparatus for exposing small laboratory animals, e.g., rats, to a test atmosphere in such a manner that the animals are exposed to a uniform concentration of the test atmosphere containing substantially no exhaled materials.The apparatus comprises, e.g., an animal holding tube capable of positioning the nose of an animal at a fixed point within the tube. The tube is provided with a test atmosphere inlet means located in the vicinity of the nose and an exhaust outlet such that the test atmosphere can be inhaled by the animal then exhausted rearward of the nose of the animal.A plurality of these animal holding tubes can be combined by connecting their inlet to a first plenum duct that is in communication with a source of the test atmosphere and connecting their outlet to a second plenum duct for exhausting substantially all exhaled materials and excess test atmosphere.