Abstract: There is disclosed a device for conducting a microbiological radiorespirometric assay. The device comprises a support member which includes a plurality of pairs of chambers. One chamber in each pair contains a radioactive labeled substrate which is capable of being metabolized by at least some microorganisms to yield a radioactive gas. The other chamber in each pair contains a means for collecting radioactive gas. The two chambers in each pair are in communication with each other by means of a passageway, which opens into each of said chambers at the upper portion thereof. There is also disclosed a method for determining whether microorganisms contained in a sample material will metabolize a radioactive labeled substrate in the device. The method comprises placing said material in contact with a radioactive labeled substrate, collecting any gas which is evolved, exposing a photosensitive material to said collected gas and determining if a spot is produced on said photosensitive material.