Background and objective Epigallocatechin gallate is the causative agent of green tea-induced asthma. To determine whether an IgE-mediated mechanism plays a pathogenetic role in this disorder, we measured histamine release after in vitro exposure to epigallocatechin gallate. Methods Subjects included eight patients (four men and four women) with green tea-induced asthma, who had been diagnosed by skin test and inhalation challenge, and eight controls (four asthmatic subjects with no previous exposure to tea dust and four healthy volunteers). Heparinized whole blood samples were taken and incubated with epigallocatechin gallate at various concentrations (final concentration range, 0.003 to 300 micrograms/mL) for 30 minutes at 37 degrees Centigrade. After centrifugation, histamine was measured in the cell-free supernatants by radioimmunoassay. Histamine release was expressed as a percentage of total histamine. A result higher than 10% was considered positive. Results In one of the tea-sensitive patients, epigallocatechin gallate did not cause histamine release. Five of the other seven patients (71%) demonstrated a positive, dose-dependent histamine release to epigallocatechin gallate. In asthmatic and normal controls, histamine release was not observed at any epigallocatechin gallate concentration. Furthermore, a significant correlation was noted between the maximum percentage histamine release and the threshold epigallocatechin gallate concentration for intradermal skin testing. Conclusion These results indicate that an IgE-mediated response is the basis for green tea-induced asthma.