Antigenic analysis of 9 strains of the Soldado virus, originating from seven different countries of Central and Northern America, Africa, Northern Europe and of the Pacific area was carried out by means of complement fixation (CF) and immunodiffusion (ID) tests. Three strains isolated from Ornithodoros (A.) capensis, including the reference Trinidad strain, were found to be related within the same relatively heterogeneous sub-group C, being characteristic for the New World. Five other strains isolated from Ornithodoros (A.) maritimus were classified to form an another, much more homogeneous subgroup M, characteristic for the Old World (related to the Ireland strain). The South Africa strain, isolated form Ornithodoros (A.), probably capensis, could not be classified in either of the above two subgroups. Thus, the Soldado virus in fact represents a complex of more or less closely related strains, but not a single virus.