Abstract: A mixture of cymene isomers, containing paracymene is subjected to adsorption-separation in contact with a crystalline aluminosilicate adsorbent which selectively retains para-cymene. Raffinate therefrom, being a para-cymene deficient mixture of cymene isomers, is isomerized to form additional para-cymene. Isomerization conditions employed to produce para-cymene, also effect formation of olefinic material. To prevent the adverse effect which olefins exhibit toward the efficiency and capacity of the zeolitic adsorbent, the isomerization effluent is subjected to hydrotreating at conditions which provide a liquid-phase operation and saturate olefins without saturation of the cymene isomers.