[α, β- 14C]Ethylbenzene produced from benzene and [1- 14C]ethanol using an acidic zeolite catalyst, HZSM-5, at 300 °C had 14C activity equally distributed between the α- and β-positions of the ethyl side chain. Thus, the carbon label in [1- 14C]ethanol was 100% scrambled in the ethylbenzene product. The same reaction at 200 °C produced [α, β- 14C]ethylbenzene with approximately 18% excess 14C activity at the α-position; this result corresponds to 82% scrambling of the carbon-14 label. Under these reaction conditions, the nearly equal α and β activity make it appear that little exchange of carbon between the ring and side chain of ethylbenzene occurred.