SUMMARYParasitism ofCorticium rolfsiiby a species ofAspergilluswas investigated by scanning electron microscopy. Within a few da afterA. terreusinfected sclerotia ofC. rolfsii, conidiophores bearing numerous conidia ofA. terreuscovered the entire surfaces of the sclerotia. Most conidiophores arose from below the surface of sclerotia, while a few of them originated from the innermost layers of cortical tissue. Microdissection revealed that sclerotial surfaces in contact withA. terreusconidiophores were flat.