The human basophil degranulation test (HBDT) studies the allergic response of effector cells. In this work, it was used in the diagnosis of anaphylactoid reactions during anaesthesia. Thirteen patients having had an anaphylactoid shock during general anaesthesia were investigated. An HBDT was performed with every suspected drug used during the anaesthesia. Ten patients had a positive HBDT and in five cases the drug involved was suxamethonium. In one case, the IgE-dependency of the accident was asserted by the ability of the plasma to sensitize in vitro alien basophils. These sensitized basophils degranulated in the presence of Althesin and suxamethonium. Passive sensitization was abolished when using plasma heated for 2 h at 56 degrees C. Two patients had a negative HBDT to 11 drugs tested. To assess the validity of these results, and to rule out unspecific degranulation, thirteen control patients who were to undergo general anaesthesia were investigated. HBDT was performed immediately before anaesthesia in a double-blind method with every drug to be used during the anaesthesia. The twelve patients who had a negative HBDT to every drug had an uneventful anaesthesia. One patient had a positive test to thiopentone and displayed bronchospasm and generalized urticaria during the anaesthesia. In conclusion, the HBDT appears to be a reliable test in the diagnosis of anaphylactoid reactions during anaesthesia.