Type-specific (presumably fiber) components of the adenovirus types 9, 9-15, 13, 15, 17, 19, and 26 were prepared by elution from DEAE columns. Their serological specificity was tested by means of complement-fixation and inhibition of indirect hemagglutination with rabbit immune sera prepared against all serotypes of group II. For comparison, HA-inhibition was also performed with directly acting hemagglutinin or dodecon antigen. Crossreactions between individual serotypes were similar in all three tests with only a few exceptions. This confirms the structural analogy of the serologically active, type-specific moiety of both components (fiber and dodecon). The induction of indirect hemagglutination by various adenovirus immune sera appears to be basically specific for the whole adenovirus group; but not all immune sera appear to contain the required antibody in sufficient strength. © 1969 Springer-Verlag.