Heterogeneous gas phase catalyst screening with catalysts applied on titer-plates is presented. It will be shown that titer-plates can as well be used for the sample preparation outside the reactor and for the catalyst testing in the reactor. For the catalyst preparation, the known wash-coating-impregnation procedure is applied. An alumina coated precursor is introduced into a manifold which utilizes the flow features of the separated wells for the impregnation of the precursor with solutions of the salts of a collection of transition metals. The impregnation liquid is flowing through the wells thus impregnating the surface of the porous gamma-alumina layers within the microchannels. Less porous coatings are realized by the simultaneous gradient sputtering process developed on the basis of the standard sputtering process.Some details about the reactor development and characterization as well as problems which arose are reported. For the description of the reactor performance, a number of coated titer-plates were tested and these results are presented. After this so-called primary screening, a second evaluation phase normally follows. In this second phase, the kinetic properties of a single catalyst shall be studied. For this purpose, a model which describes the fluidic behavior of the reacting gas in microchannels was developed. Applying the model will give further insights into the underlying reaction kinetic of a single selected catalyst in the so-called secondary screening phase. (C) 2003 Elsevier Science B.V. All rights reserved.