Electron microscopy of tissues from two necropsies carried out in the Sudan on patients with Ebola virus infection identified virus particles in lung and spleen, but the main concentrations of Ebola particles were seen in liver sections. Viral precursor proteins and cores were found in functional liver cells, often aligned in membrane-bound aggregations. Complete virions, usually found only extracellularly, were mainly seen as long tubular forms, some without cores. Many tubular forms had 'enlarged heads' or 'spores' and some branched and torus forms were identified. The size and structure of the Ebola virus forms appear to be virtually indistinguishable from those of Marburg virus.