A method of investigation or control of catalysts or catalyst reactions wherein a gas or gas mixture is brought into contact with the catalyst (12). The properties of the catalyst and/or the progress of the reaction depending on the catalyst are determined or controlled by applying an electric field between the catalyst (12) and an electrode (10) which is arranged in the gas atmosphere spaced from the catalyst.The size of a corona current thereby produced between the catalyst and the electrode is measured and/or adjusted.