Catalyst deactivation runs were carried out in a flow reactor using bitumen and its maltene fraction as feeds in heptane solvent. Catalytic activity tests, using a mixture of model compounds, were performed to evaluate hydrogenation and C-N hydrogenolysis activities both directly after the aging run and again after the same aged catalyst had been posttreated by extraction with chloroform and resulfided. Two types of carbonaceous deposits were identified on the aged catalysts. One type, deposits left on the catalyst directly after the aging run, contained relatively large amounts of polymer-like material and caused significant losses in catalyst surface area. Catalytic activity was best related to residual, unblocked surface area and some poisoned sites. The second type, deposits remaining after extraction of the aged catalyst, was typical of conventional coke and did not block any pores. Subsequent activity tests showed activities were related to catalyst coke content.