Hyphae of virulent (v) E. parasitica isolate 16-15-1 (West Virginia [USA]) and hypovirulent (hv) isolate Ep-4 (France) were preserved by freeze-substitution, embedded and longitudinally sectioned to describe and compare their subcellular structure. General ultrastructural features of both were similar. Apical vesicles and uncoated microvesicles were common constituents of the extreme hyphal apex. Abundant membranous material also was seen in this region in some tip sections of hv isolate Ep-4. Filasomes were located along the lateral hyphal wall just behind the apex and one was observed to be fused with the plasmalemma. Golgi cisternae were numerous in the tip area and appeared very flat and fenestrated and often were closely associated with mitochondria. Components of the vacuole system were variously shaped, totally electron dense in young hyphae and lighter with discernible inclusions in older hyphae. Spherical, membrane-bound virus-like particles (VLP), 51-78 nm in diameter, were observed in tip cell of hv isolate EP-4, but not v isolate 16-15-1. The VLP may be responsible for hypovirulence in the Ep-4 isolate. Endoplasmic reticulum cisternae contact in hyphae of Ep-4 may have been related to the presence of VLP.