SummaryMyeloblasts of avian myeloblastosis treated with colloidal gold solution developed numerous cytoplasmic, electron-dense gray bodies and ingested gold and extracellular virus particles in microvesicles. Both kinds of particles were transferred to the gray bodies. The gray bodies and associated vesicles and vacuoles resembled elements of lysosomal systems occurring in other cells. The findings explained the presence of virus in gray bodies alternative to the previous interpretation of virus synthesis in the bodies.