Abstract: A physically intermixed catalyst system comprising two distinctly different catalytic particles, the first of which is a hydrodenitrification and/or hydrodesulfurization catalyst and the second of which is a relatively active hydrocracking catalyst, wherein the catalyst particles of both catalytic components are substantially the same size, that is the effective diameter of each catalyst component is substantially the same. The catalyst system of the present invention can be layered with unmixed catalysts. The novel systems of the present invention have been found to provide surprisingly good selectivity for liquid products and stability against catalyst fouling when used in combined hydrotreating and hydrocracking applications, and can therefore be used to provide a stable catalyst system which offers even heat distribution and reactor control in such applications.