A screening system is described for identifying fungal antagonists from soil which are effective in controlling seed-borne Fusarium culmorum on wheat (T. aestivum L.). The procedure comprised three consecutive in vivo tests done under controlled conditions using three different plant growing media. Altogether 1701 fungal isolates from Finnish field soils were screened for biocontrol activity. 210 fungal isolates that had advanced to various stages in the screening system were also included in a field experiment. The isolates that were the most effective in controlling seedling blight under natural conditions belonged to the genus Gliocladium. The screening tests separated Gliocladium spp. rather clearly from the rest of test fungi and thus the overall agreement among the results was good. The assays run under controlled conditions did not efficiently predict which of the Gliocladium isolates would be best in protecting wheat seedlings under field conditions.