The formation of predominating C-3 species during the conversion of ethanol on H-ZSM-5 catalyst was examined as a function of temperature, time on stream and space velocity. The trends observed indicated that propene was formed from the cracking of larger olefins, possibly 4-methylpentene, and not as an intermediate between C-2 and C-4 production. The parallel formation of propene with naphthenes and aromatics resulted in significant hydrogen-transfer activity leading to propane, while ethylene and butenes played a much less significant role in the process.