Eight different filovirus isolates, representing major episodes of filovirus hemorrhagic disease, were propagated for structural and antigenetic analyses of their glycoprotein (GP). Carbohydrate analysis revealed that N- and O-glycosylation are features of filovirus GPs. Oligosaccharide side chains differed in their sialylation pattern and seemed to be cell line-dependent. Marburg virus (MBG) isolates are clearly distinguished from Ebola (EBO) and Reston viruses by a lack of terminal sialic acids when propagated in E6 and MA-104 cells. It was also determined that GP-specific antisera failed to show any cross-reactivity between MBG isolates and other filoviruses. These data, together with prior findings, indicate that the genus Filovirus can be divided into a MBG group and EBO group.