We used 140 IgG complement-fixing blood group alloantibodies of 17 different specificities in tests to determine whether anticomplement antibodies are still necessary in antiglobulin reagents to be used in indirect antiglobulin tests. Anti-Rh and other IgG noncomplement fixing antibodies were excluded from the study. A polyspecific antiglobulin reagent that contained anti-IgG and anticomplement antibodies, and an anti-IgG reagent containing the same level of anti-IgG as the polyspecific one, were compared. Titrations with some of the antibodies were repeated with only the polyspecific reagent. With each antibody, studies were done with complement activation blocked, and compared with results in which it was allowed to proceed. We found that 42.9% of the antibodies were detected at a higher dilution, and 64.3% of them were detected with a higher titer score, when the poly-specific antiglobulin serum containing anticomplement antibodies was used. We conclude that anticomplement antibodies are indeed still essential for the correct performance of indirect antiglobulin tests.