The effects of hydrogen in the catalytic reforming of n-hexane, which consists of successive isomerization, cyclization, hydrogenolysis, and dehydrogenation, were examined using a palladium membrane reactor through which the hydrogen could be selectively removed from the reacting mixture at temperatures of 250-350 degreesC and atmospheric pressure. When no hydrogen was added to the feed, significant decreases with time on stream in both the conversion and the activity of catalyst were observed once the flow of sweep gas was started to remove the hydrogen produced in the reforming reaction. This shift in the unexpected direction was found to occur when the hydrogen required to initiate the isomerization step, i.e., the so-called spillover hydrogen, was lacking. When hydrogen was premixed into the feed, stable conversions were obtained, and then removal of the excess hydrogen resulted in an improvement in the conversion of n-hexane.