Abstract: A catalyst unit for an exhaust gas catalyst, having a ceramic catalyst body, and a metallic housing which encloses the catalyst body at least in some sections perpendicular to a gas throughflow direction. At least one bearing mat positioned between the catalyst body and the housing perpendicular to the throughflow direction. The catalyst body is retained in the housing via a force-closed press fit with the intermediate arrangement of the or each bearing mat such that, when seen in the throughflow direction of the catalyst body, the press fit between the housing and the catalyst body is formed exclusively at defined axial positions, the housing having groove-like depressions at the defined axial positions for reducing in some sections the inner cross-section of the housing, and the press fit between the housing and the catalyst body being formed exclusively in the region of the groove-like depressions.