Hypha! interactions between either Trichoderma harzianum or T. hamawm, and Sclerotium rolfsii or Rhizoctonia so/ani were observed by scanning electron microscopy. Trichoderma spp. auached to the host either by hypha! coils, hooks, or appressoria. Lysed sites and penetration holes were found in hyphae of the plant pathogenic fungi, following reinoval of parasitic hyphae. High 13-(1,3) glucanase and chitinase activities were detected in dual agar cultures when 1: harzianum parasitized S. rolfsii,