Alkyl aromatic hydrocarbons useful as chemical raw material, solvents and the like are provided in high purity by hydrocracking of a fraction rich in alkyl aromatics and lean in aliphatic hydrocarbons over a particular zeolite catalyst associated with a hydrogenation/dehydrogenation component. The charge stock is characterized by substantial absence of hydrocarbons lighter than benzene. The technique is particularly well suited to production of maximum xylenes from a fraction containing higher boiling and lower boiling alkyl aromatics.