Background: The flow cytometry CD63-based basophil activation test (Basotest(R)) has already been validated for the diagnosis of immediate-type allergy such as venom, house dust mite or cypress pollen allergies. The aim of this study was to evaluate the performance ( specificity and sensitivity) of Basotest in the diagnosis of natural rubber latex allergy. Methods: We included 46 latex allergic patients ( clinical symptoms of latex allergy, positive latex skin prick tests and/or latex specific IgE) and 33 control subjects and performed Basotest on all subjects. Results: The sensitivity and specificity of Basotest were 84.8 and 87.9%, respectively, when we considered the theoretic cut-off at 15% of CD63-positive cells. Using ROC curves, the optimal cut-off was evaluated at 22%, for which sensitivity and specificity were 79.3 and 96.7%, respectively. Conclusion: The Basotest is a reliable test in addition to clinical history and tests already validated ( such as skin prick tests and specific IgE) to confirm the diagnosis of natural rubber latex allergy. Copyright (C) 2005 S. Karger AG, Basel.