Viruses grouped in the family Potyviridaeare long flexious rod-shaped viruses and cause the most damage of all plant vims groups. They possess a single stranded positive sense RNA genome that encodes a single polyprotein product which yields eight or more proteins by secondary processing. Considerable efforts have been made to transform plants with DNA or RNA sequences of these proteins in hopes of obtaining pathogen-derived resistant plants. Hull has suggested that a close assessment of the risks involved in field release of transformed plants would be desirable. However, to our knowledge, there have been no published reports regarding properties of viruses that do infect some transformed plants. We describe here an ultrastructural appearance of transgenic plant cells infected by potato virus Y (PVY) (ATCC PV No. 50; PVY-50) and unusual mitochondrial aggregation with the virus.