A Streptomyces sp. strain named C/33-6, previously isolated from soil, presented a strong and specific antagonistic effect against toxigenic fungi. This action was attributed to a proteinaceous compound (molecular weight estimated to be 14 kDa) present in the supernatant of the culture of strain C/33-6, which was sensitive to proteinases (elastase, pronase E, proteinase K) and prolongated heat treatment (100degreesC, for 20 min). This compound showed non-chitinolytic fungicidal activity.