Measuring antibodies to Bordetella pertussis antigens is mostly done by enzyme-linked immunosorbent assays (ELISAs). We compared the performance of five commercially available ELISA kits with the help of 65 serum specimens which were repetitively tested for evaluation of the kits. The specimens contained 20 paired serum samples from patients with clinical pertussis, 15 samples were from children vaccinated with a diphtheria-tetanus-acellular pertussis vaccine, seven specimens were taken from an interlaboratory comparison of ELISAs, and there were three reference preparations from the Food and Drug Administration's (FDA's) Laboratory of Pertussis and from our laboratory. Reference values were obtained from the FDA or from results obtained with an in-house ELISA. Commercial ELISAs were compared with respect to their reproducibility and variability, their ability to detect significant titer rises in paired serum samples, their ability to detect an immune response after vaccination, and the comparability of semiquantitative and quantitative results. Reproducibility was generally good (>89%), intra-assay variation ranged from 2.4 to 28.7%, and indeterminate results were recorded in up to 18.5% of all specimens. Most kits correctly identified the antibody response to an acellular pertussis vaccine. None of the commercial kits identified all cases of pertussis correctly, and the sensitivity ranged between 60 and 95%. All five commercial ELISAs showed great discrepancies when comparing semiquantitative results and contained obviously different antigen preparations. Our data suggest that the five commercial ELISAs tested here need further improvement and standardization.