A 24-kDa protein that elicits ethylene production and necrosis in leaves of dicotyledonous plants was previously purified from culture filtrates ofFusarium oxysporumSchlechtend:Fr. f.sp.erythroxyli. Antisera to the denatured 24-kDa protein detected 2.5 ng of the 24-kDa protein on Western blots at 100 000-fold dilutions. The antisera cross-reacted with a 24-kDa protein on Western blots of culture filtrates from three otherF.oxysporumformae speciales. Of sevenFusariumspecies, onlyF.oxysporum,F.acuminatumEllis and Kellerm., andF.avenaceum(Fr.:Fr.) Sacc. isolates produced an antigenically related 24-kDa protein. Although there were differences in the profiles of proteins extracted from stems of coca (Erythroxylum cocavar.cocaL. Lam.) infected withF.oxysporumf.sp.erythroxylicompared with uninfected stems, antisera to the 24-kDa protein did not cross-react with any proteins from the infected coca stems. For the fungal isolates studied, the best medium tested for production of the 24-kDa protein contained 1% sucrose and 1% asparagine. Biological activity of theF.oxysporumculture filtrates on sweet basil leaves was consistently correlated with the presence of the 24-kDa protein. Production of the 24-kDa protein was limited in cultures containing pectin or cellulose as the primary carbon source, or in cultures lacking sucrose or casamino acids. Water-soluble extracts from coca stems inhibited production of the 24-kDa protein, whereas cellulose and pectin did not. Components produced by the plant may limit production of the 24-kDa protein in infected plant tissue and thereby limit the response of the plant to the fungus. These results suggest the 24-kDa protein does not function in the symptomatic phase of theF.oxysporumf.sp.erythroxyli–coca disease interaction.Key words:Fusarium oxysporum, toxin, elicitor.