In this note, the authors present evidence of competitive reaction in intrazeolitic media, showing that coreactants in the feed can induce rate and selectivity modifications of a primary reactant. The specific reaction considered is the hydroisomerization/hydrocracking of n-hexane over Pt/H-mordenite in the presence of an aromatic cofeed. In earlier work the authors have found that the presence of benzene in the feed significantly inhibits the reaction of the paraffin. In this work, they further examine such competitive reaction over Pt/mordenite by considering the effect of a series of aromatics on n-hexane reaction rate and isomer selectivities. The aromatics used include benzene, toluene, p-xylene, and mesitylene. The objective was to determine if correlations could be found among the aromatic size relative to zeolite pore size, the inhibition of the hexane reaction, and modifications to isomer selectivities. 8 references.