The effect of both total pressure and hydrogen partial pressure during the n-hexane isomerization on Pt/SO42--ZrO2 at 200 degrees C and 4 h(-1) weight hourly space velocity was studied. Total pressure was varied between 1.0 and 10.0 kg cm(-2); different hydrogen partial pressures were obtained by dilution with nitrogen keeping the total pressure at 6 kg cm(-2). The n-hexane isomerization activity increases when increasing either total pressure or hydrogen partial pressure. Methylpentanes are the C-6 isomers formed in major proportion and the 2-methylpantane/3-methylpentane ratio practically reaches the equilibrium value in most of cases. Isomerization is always accompanied by hydrocracking. Hydrogenolysis products were not observed, the main cracking products being propane, isobutane and isopentane; then, the cracking product distribution cannot be interpreted by considering an intramolecular rearrangement of carbocation intermediates. A slight deactivation takes place with time-on-stream. The lifetime of surface intermediates is longer in the absence of hydrogen or at a low hydrogen partial pressure; it allows oligomerization and cracking to prevail at short times and polymerization and coke formation at long times.