In Australia, pertussis whole cell IgA has traditionally been used extensively for a single sample serological diagnosis of pertussis. Due to specificity issues regarding whole cell and filamentous haemagglutinin assays, the Public Health Laboratory Network suggests that it is likely that pertussis toxin IgG assays will become the test of choice for the serological diagnosis of pertussis. However, the actual cut-offs are far from clear. The Virology Department at SA Pathology utilises real-time PCR to detect IS481 for the molecular diagnosis of Bordetella pertussis. A retrospective data extract and sample search resulted in 441 serum samples, collected from 372 IS481 PCR positive patients, being analysed using the EuroImmun anti-pertussis toxin IgG, IgA and IgM ELISAs. The serology sample collection dates ranged from up to 558 days prior to and 525 days after the positive PCR result. In addition, 245 “pertussis negative” samples, were also analysed. Both the pertussis toxin IgM and IgA assays were deemed to be highly specific yet both exhibited poor sensitivity. Therefore the pertussis toxin IgG assay was determined to be the most suitable assay for the serological diagnosis of pertussis. Furthermore, for the IgG assay, a dual cut-off of 40 IU/mL and 100 IU/ml was deemed to be the most sensible approach to result interpretation.