Fourteen patients who had had a life-threatening reaction within a few minutes after receiving propofol (Diprivan) were investigated for anaphylaxis 4-6 weeks after the incident. Three kinds of immunologic tests were carried out: skin tests (prick tests and intradermal tests with the drugs used and Intralipid, the solvent for propofol), a leukocyte histamine release test, and a radioimmunoassay (RIA) of immunoglobulin E (IgE) against propofol and muscle relaxants, when they had been given with propofol. It had been previously shown that these were always negative in patients anesthetized with propofol without any complications. Thirteen of the 14 patients had at least one positive test supporting hypersensitivity to propofol; 2 patients had three tests positive; 4 had two tests positive; and 7 had one test positive. The skin tests with Intralipid were negative in 4 patients whose tests with propofol were positive. Two patients who had been given muscle relaxants at the same time as the propofol had positive IgE-RIA to both drugs. In one patient, results of all the tests remained negative, and the mechanism involved in the reaction remained unidentified. It is note-worthy that 9 patients of 14 had allergic histories that were known before the anesthetic (atopy; allergy to antibiotics, muscle relaxants, lidocaine, colloids) and that none of the patients had ever received propofol or Intralipid before. It is possible that the IgE that linked abnormally with the propofol had specific binding sites for the phenyl nucleus and the isopropyl groups, which are present in propofol and many other drugs.(ABSTRACT TRUNCATED AT 250 WORDS)