An indirect immunofluorescence test was employed to detect and quantitate serum antibodies to trachoma-inclusion conjunctivitis (TRIC) antigens of 6 types. This test was markedly more specific and sensitive than the group-reactive complement-fixation test. Striking differences in antibody patterns were detected in different groups of patients suffering from acute or chronic TRIC infections. Among Tunisian children 67% had antibody which was primarily directed against TRIC types A or C. Among American Indian students, 33% had antibody which was directed mainly against TRIC types B, D, or E, but not against A or C. Most San Francisco patients with acute oculogenital TRIC infection had antibodies broadly reactive with all 6 TRIC antigen types A to E. Some immunologic and epidemiologic implications of these results are discussed.