Structural studies on stealth viruses have confirmed the tissue culture conclusion that they represent a grouping of atypically structured viruses, rather than a single virus entity. The best studied isolate has a fragmented genome partially derived from African green monkey simian cytomegalovirus and also partially derived from various cellular genetic sequences. The virus is genetically unstable, indicative of an error prone replication. Infected cells are metabolically impaired because various energy generating and other cellular resources are presumably diverted towards the synthesis of viral components at the expense of normal functions. Virus and altered cellular products can also directly affect various metabolic functions. Some of the cellular toxins are identifiable in stealth virus cultures.