Abstract: An apparatus for exposing laboratory animals to a gas or vaporous substance directly to the nose of the animals and hence the respiratory system of laboratory animals includes concentric inner and outer manifolds. The inner manifold is provided with a plurality of distribution tubes extending radially outward from the manifold, each tube having a horn shaped end.The outer manifold is provided with a plurality of apertured connectors through which the distribution tubes extend. The apertured connectors partially support animal holders such that the nose of an animal within each animal holder is positioned proximate to the horn end of one distribution tube. A gaseous substance is introduced from the lower end of the inner manifold, travels upwardly to the distribution tubes, through the tubes to the animal's noses, then passes through the apertured connectors where it enters the outer manifold. The vaporous substance is drawn upwardly out of the outer manifold.