Cooperating with pediatricians in private practice and in hospitals, we tried to evaluate the diagnostic relevance of three serological methods for the detection of antibodies to Bordetella pertussis. The tests employed were a microagglutination, a complement fixation and an enzyme-linked immunoassay (ELISA) to measure specific IgG, IgM, IgA and IgE with whole B. pertussis phase I cells as an antigen. In addition, sera were tested for complement-fixing antibodies to respiratory-syncytial (RS) virus. Microbiological procedures also were used to detect B. pertussis in pernasal swabs. Single sera from 259 children and adults with suspected whooping cough were tested. Of these 117 samples did not contain any measurable antibodies to B. pertussis (45%) and only four sera of this group exhibited complement-fixing antibodies to RS-virus (3%). Antibodies to B. pertussis could be found in the sera of 142 patients. In this group, complement-fixing antibodies to RS-virus were detected in 23 sera (16%). Comparing the methods used to measure antibodies to B. pertussis showed that the ELISA was the most sensitive test, followed by complement fixation and microagglutination. In 21 additional cases, paired sera and several swabs could be obtained from individual patients. These data allowed us to follow the antibody response to B. pertussis during whooping cough, which seemed to be characterized by a relatively late onset with a subsequent rapid increase of initially IgM and IgA and then IgG antibodies. Analogously, the titers of complement-fixing and agglutinating antibodies increased during the later stages of the disease.(ABSTRACT TRUNCATED AT 250 WORDS)