Investigations into the nature of ethylene production by Bipolaris sorokiniana and B. sorokiniana infected leaf blades of Poa pratensis were the main objectives of this research. Characteristics of the assay for 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, the enzyme that controls ethylene formation in higher plants, were also studied;Protein was found to interfere with the determination of ACC. Interference was partly overcome by modifying the assay procedure;Methionine (Met) and ACC stimulated ethylene production in B. sorokiniana. ACC was less effective than Met in stimulating ethylene production. Met decreased fungal growth and sporulation;Infection of P. pratensis by B. sorokiniana resulted in necrosis of the afflicted tissue. It was speculated that the host-pathogen interaction involved the contribution of the fungal ACC synthetic pathway and the ethylene forming pathway of the host.