High levels of protection against infection from Blumeria graminis Esp. hordei in the susceptible barley cv. Pallas were obtained by pretreatment with mycelial extracts or culture filtrates from seven different fungi (Bipolaris oryzae, B. sorokiniana, Drechslera teres f. maculata, Fusarium culmorum, Trichoderma harzianum, Pythium ultimum and Rhizopus stolonifer). Three mycelial extracts from the taxonomically different fungi B. oryzae, A ultimum and R. stolonifer were selected for detailed study. In general the number of colonies formed was reduced by 70-98% compared with controls. Furthermore, the few colonies that developed on treated leaves were generally smaller and showed reduced spore production. Protection was limited to the area of the leaves treated with mycelial extracts and a systemic effect could not be detected. No differences in the protection level were observed when treatment was conducted between 2 h and 3 days before inoculation. It is suggested that components in the mycelial extracts interacted directly with B. graminis and that this antifungal effect was responsible for the observed protection. However, indirect effects of the mycelial extracts mediated by locally induced resistance cannot be precluded.