To evaluate whether pertussis induces the development of allergy, a prospective study was performed in 25 children aged 0.8-12.2 years. The patients underwent allergy diagnostics during pertussis infection and at a follow-up visit 8-14 months later. Diagnostic criteria included the medical history of the patients and their families, a modified skin prick test, measurement of serum IgE and radio-allergosorbent test screening for specific sensitizations. At the time of pertussis, serum IgE concentration in the study group was 62 +/- 30 kU/ml. At the follow-up visit, there was a significant increase in serum IgE to 137 +/- 51 kU/ml, which was also significantly higher than IgE in an age-matched control group. Children at a significantly higher risk for developing IgE increase or new allergic sensitizations were those with a family history of allergy or potentially allergic disease in their personal history. Our results indicate that pertussis may induce IgE production in affected children.