Three distinctive types of viral inclusion bodies were identified in hantavirus-infected cells by thin-section electron microscopy. The inclusion bodies, designated granular, granulofilamentous, and filamentous, were intracytoplasmic and closely associated with the rough endoplasmic reticulum and Golgi cisternae. Virus specificity of the inclusions was verified by immune colloidal gold and immunoperoxidase labeling. The inclusion bodies were a common morphological marker for 13 strains of hantaviruses studied, irrespective of their origin.