The selective oxidation of isoprene to citraconic anhydride over variadia-supported catalysts is used as a test reaction for the comparison of different reactors. A metal microchannel reactor reveals a behaviour that indicates a better isothermicity than a laboratory-scale tubular reactor. However, the blank activity of the stainless steel microchannels with their high surface-to-volume ratio seems to decrease the catalytic performance. A ceramic microchannel reactor has an intermediate isothermicity and less blank activity. From the experiments, additional features like pressure drop or mass transfer can be evaluated. The generic differences between microchannel reactors and conventional laboratory-scale reactors are discussed in the framework of recent literature. It becomes obvious that microchannel reactors may currently still suffer from problems like high blank activity or intricate catalyst application, but do have intrinsic advantages like the high isothermicity. On a general note, the different scaling of length, surface area and volume makes a straightforward comparison between microchannel reactors and conventional reactors far from trivial.