The conversion of,l-hexane and 2,2,4 triMe-pentane was studied at 723 K on a USY-zeolite (Si/Al: frame=30; bulk=2.7) in an electrobalance reactor with external recirculation. The influence of the coke content on the reaction paths involved in the conversion of paraffinic model components was evaluated. Coke formation from propylene and i-butene, the main olefinic products formed during the conversion of the two paraffinic model components, was investigated. Under the conditions used, an increase in the molar WC ratio of the products as a function of coke yield can be observed due to hydride transfer reactions with coke. Coke molecules cannot be considered as being inert with respect to the cracking reactions and their formation leads to the occurrence of reactions that can strongly influence the catalyst performance. In particular, the potential of coke molecules to form highly delocalized carbenium ions and their ability to act as hydride donor towards surface carbenium ions provides reaction paths to paraffinic reaction products. The effect of coke is not identical for all the elementary reactions involved in the conversion of the paraffinic model components.