In contrast to the usual two-liquid-phase process the hydrogenation of benzene is carried out in a continuously operated slurry (CST-) reactor containing only one liquid phase, an alkaline aqueous zinc chloride solution in which a ruthenium lanthanoxide catalyst is suspended. This new procedure gives rise to an improvement of reaction engineering and makes possible the direct measurement of reaction rates for detailed kinetic studies. It could be shown that cyclohexane is only formed by consecutive hydrogenation of cyclohexene. The rates of benzene and cyclohexene conversions are mutually independent of the partial pressures of cyclohexene and of benzene suggesting different sites of benzene and cyclohexene hydrogenation. Conclusions for optimal reaction engineering are drawn.