Virus isolation.Virus isolation is a basic, simple, and sensitive method for diagnosis of EHF and MHF. EBOV and MARV grow well in a large variety of cell lines, but Vero cells and Vero E6 cells are commonly used. Specimens such as blood must be sent to BSL-4 laboratories, which are located in developed countries, from an outbreak area, which is often very remote. The shipment of specimens for virus isolation under favorable conditions (cold chain during the period from shipment to arrival) is often difficult. Therefore, diagnostic criteria based on virus isolation alone will not yield an etiologic diagnosis. A panel of monoclonal antibodies to the recombinant NPs (rNPs) of Zaire EBOV, Reston EBOV, and Lake Victoria MARV was established by our group (20, 39, 40, 44). Monoclonal antibodies specific only for NP of Zaire EBOV, for NP of Reston EBOV, for NPs of Zaire and Sudan EBOV, for NPs of Zaire and Reston EBOV, and for NP of Lake Victoria MARV alone were developed. By using these monoclonal antibodies, it became possible to serologically identify the species of EBOV and MARV isolates.