Ethylene production from stems of seedlings of species in sections Quercus, Q. serrata and Q. crispula, and section Cerris, Q. variabilis and Q. acutissima, was compared after inoculation with Raffaelea quercivora. Section Quercus species produced ethylene rapidly within 3 days of fungus inoculation, although the ethylene emanation decreased beginning on day 7. Rapid ethylene production also occurred within 3 days in section Cerris species. Q. variabilis maintained compara-tively high ethylene production for at least 2 weeks, even in uninoculated seedlings.