Electron microscopic evidence for parainfluenza type III/retrovirus phenotypically mixed particles

Sublines of malignant permanent human fibroblast cell lines were shown to be infected by a type-D retrovirus (PMFV) and by a parainfluenza virus type III in an earlier study (2, 6). Careful electron microscopical investigations of these sublines have proved "viral structural elements" of both viruses in the same cell. We obtained electron microscopic evidence--though rarely--for parainfluenza type III/PMFV mixed-particles.