The sensitivity of usual IgE-RIA for detecting seric anti-neuromuscular blocking drug (NMBD) IgE antibodies is low. Our group and other authors have proposed quaternary ammonium compounds other than NMBD for the preparation of sepharose solid drug phase. These compounds cannot be cyclohexenyl derivatives in order to prevent hydrophobic interactions with seric hydrophobic IgE. Allergic reactions against cyclohexenyl derivatives such as propofol could be linked to a non-specific hydrophobic binding of the drug to hydrophobic seric IgE. Such hydrophobic IgE are seen in 30% of atopic subjects, in 41% of patients with drug allergy and in 100% of those allergic to propofol. The latter had also anti-quaternary ammonium IgE in 5 out of the 8 cases studied. These NMBD antibodies could bind to the quaternary-ammonium ion of the lecithins from Diprivan micelles.