Abstract: A microreactor is described which is especially designed to analyze small solid samples, such as thin film catalyst. It includes (a) a horizontal tubular reaction vessel for receiving an article for testing, one end of the vessel being closed and the other end being connected to a ball valve end flange, (b) a horizontal shelf within the reaction vessel adapted to receive and support the article for testing, (c) gas inlet means for introducing gas into the vessel, (d) gas outlet means for removing gas from the vessel, (e) sensing means for sensing the temperature within the reaction vessel, (f) means disposed outwardly of the vessel and in heat-conductive relation to the outer surface thereof for heating the vessel, and (g) releaseable gripper means for delivering the article for testing through the ball valve and into the reaction vessel and for releasing the article onto the shelf.