The discovery of IgE antibodies to neuromuscular blocking drugs, to thiopentone and narcotics, particularly morphine, reinforced earlier beliefs formed from skin test and other clinical findings that many << anaphylactoid >> reactions to drugs were true type 1 immediate hypersensitivity reactions. Immunochemical studies established the fine structural specificities of the drug-reactive IgE antibodies and provided an explanation in molecular terms for a number of observed clinical cross-reactions. Subtleties in interpreting relationships between skin tests and IgE radioimmunoassays are pointed out and mechanisms of drug-induced mediator release, persistence of IgE antibodies and the nature of the sensitizing sources are discussed.