One hundred severe peranesthetic accidents occurring in hospitals in the eastern part of France were tested between 1975 and 1980 at the Immunological Unit of the University Hospital in Nancy. Tests were carried out "a posteriori"; mean time: three weeks after the accident (extremes: one week to one year). A second battery of tests was carried out in 35%, and a third one in 8% of the patients. Anaphylaxis was differentiated from anaphylactoid reactions be means of the tests. Responsible drugs were determined by intradermal testing, by the human basophil degranulation test and P.K. tests. Predisposing factors were studied: atopy (IgE dosage), increase of histamine release (intradermal testing with 48/80), abnormal receptivity to histamine (intradermal histamine), spasmophilia (electromyography recordings). The results show that 42 accidents were due to true anaphylaxis (one of them due to IgG); 48% of the reported accidents were due to succinylcholine. Some of the predisposing factors, in the tested population, are found in a higher proportion than in the French population as a whole; atopy, hypersensitivity to histamine, previous drug allergy, spasmophilia.