Six randomly selected isolates of Thielaviopsis basicola were found to contain spherical virus-like particles (VLPs) approximately 40 nm in diameter. One isolate, ATCC 34114, selected for further analysis contained a complex of VLPs that sedimented as eight or more bands in sucrose density gradients and contained five size classes of double-stranded RNA. Five discrete precipitation lines were obtained in immunoelectrophoresis, which indicated that this isolate of T. basicola contains five distinct species of VLPs.