The majority of patients with anaphylactoid reactions (AR) under general anaesthesia showed histamine release from basophil leucocytes (HRL) by neuromuscular blockersin vitro (none in normals) and high levels of serum IgE antibody (detected by the ‘new’ paper radioallergosorbent test, RAST; little or none in normals) which reacted with the quaternary ammonium group of choline, and less frequently of alcuronium, strongly suggesting that IgE antibody, HRL and AR are related. Skin tests on their own are of limited value.