The processes of assembly, budding and release of spherical viruses have been extensively studied [25, 26, 27] and it is well established that spherical enveloped viruses are produced by budding away from the cytoplasm in a process that is related and topologically equivalent to the formation of small vesicles in multivesicular bodies [28, 29] . In contrast, the basic steps of assembly and release for large, filamentous, enveloped particles such as the filoviruses are poorly understood. EM studies have shown MARV and Ebola virus particles protruding perpendicularly from the cell [23, 30] . These observations, together with similar findings of protruding intermediates of other important filamentous or rod-shaped viruses such as rabies virus [31] , influenza virus [32, 33, 34] , or vesicular stomatitis virus (VSV) [35] have led to the suggestion of a vertical ''rocket-like'' mode of budding. Ebola virus NCs have been seen associated parallel to the PM [36] , leading to the suggestion that a second, horizontal, ''submarine-like'' mechanism is the major mode of budding. This unusual mechanism has not been described for any other virus.