Onboard tests of an oxide (CoOx) and a molten mixed oxide catalyst (CoPbOx) supported on cordierite wall flow filters (Coming Durotrap CO EX80) were performed on rollers with a 1.9-1 light duty vehicle for three different driving conditions including two constant speeds with different loadings and a standard European cycle (NEDC). The balance point temperatures obtained in these tests were used to compare the catalytic activity under onboard conditions with laboratory measurements. Onboard tests showed similar catalytic activities with the previous micro-reactor experiments performed in "loose contact" mode [D. Uner, M.K. Demirkol, B. Dernaika, Appl. Catal. 13: Environ., in press]. The concentration profiles of the active layer determined by SEM-EDX analysis after use and after aging revealed that the mobile component, PbOx, migrated in the flow direction and accumulated at the closed end of the channel. There is no direct evidence for the evaporative loss of PbOx. Regions of high activity indicated by low carbon amounts with unique Pb-Co ratios were determined by SEM analysis. (c) 2005 Elsevier B.V. All rights reserved.