A process for the production of an isomerate with a RON that is at least equal to 80 and that contains less than 1% by weight of aromatic compounds, starting with a fraction consisting mostly of hydrocarbons with 7 carbon atoms, and containing paraffins, naphthenes, and aromatic compounds in any proportion is described. Said process uses at least one isomerization unit, at least one unit for opening naphthene rings, and at least one separation unit; these units are combined in such a way as to recycle, to exhaustion, methyl cyclohexane, toluene, and normal paraffins and monobranched paraffins.