A liquid medium was developed for in vitro germination and growth of rye (Secale cereale L.) pollen. Addition of style extracts from ‘Otane’ wheat which were incompatible with rye selectively inhibited pollen tube growth, compared with compatible ‘Chinese Spring’ wheat. Dialysed extracts were most suitable for incompatibility assays. Rye pollen was also selectively inhibited by extracts from self–compatible styles. Intergeneric incompatibility in wheat appears to be controlled by inhibitory style proteins.