The pore topology of a recently synthesized zeolite IM-5 has been determined by means of catalytic test reactions, i.e., n-decane hydroisomerization-cracking, m-xylene isomerization-disproportionation, n-hexadecane isodewaxing, and adsorption-microcalorimetry of molecules with different sizes and shapes (n-hexane, toluene, m-xylene, and 1,3,5 trimethylbenzene). It has been found that the channel network consists of a system of unidirectional 10 MR with lobes or side pockets, or crossing 10 membered ring pores with a pore diameter somewhat smaller than those in ZSM-5, This structure offers interesting shape selectivity features for catalytic reactions. (C) 2000 Academic Press.