IgM, IgA, and IgG antibodies to Bordetella pertussis were measured in paired sera from 34 patients who were culture-positive for pertussis by enzyme-linked immunosorbent assay (ELISA) with disrupted B. pertussis bacteria, purified pertussis toxin, or outer membrane proteins (OMP) as antigens. Paired sera from 50 patients with other respiratory infections were used as controls. The sensitivities of the assays from paired sera were 61%, 90%, and 90% and specificities were 98%, 92%, and 72%, respectively. Of the patients culture-positive for pertussis, 68% had positive levels of antibody to pertussis toxin antigen in their first serum samples, obtained at the same time as samples for culture. Infants had antibody responses to pertussis toxin antigen, in contrast to weak antibody responses measured by B. pertussis antigen. The results from this study indicate that ELISA, especially measuring pertussis toxin IgA, is a valuable additional tool for diagnosing pertussis and can be used as a complementary test with cultures.