Colletotrichum musae isolate CM100 is capable of producing ethylene in vitro on methionine-supplemented basal medium. This isolate also produced ethylene on peel extracts of banana fruit that contained methionine at 0.31-0.42 mu mol/g fresh weight. Ethylene production rates by fresh banana peel strip explants and by whole fruit were not significantly increased after C. musae infection compared with non-infected control tissues. Moreover, exogenous application of methionine did not increase either ethylene production or disease severity on banana peel strips or on whole fruit. Overall, these findings suggest that C. musae could not utilise methionine in the host tissue for ethylene production. Autoclaved banana peel strips produced negligible amounts of ethylene compared with non-autoclaved tissues irrespective of C. musae infection. This observation suggests that ethylene evolved by C. musae-infected banana tissues is of host origin. Considered collectively, the results of this study indicate that the ability of C. musae to produce ethylene in vitro does not play a role in its pathogenicity in planta.