A case is reported of isolated bronchospasm occurring during the removal of two hydatid cysts in the same patient at the same time. This 44 year old man already had had a hydatid cyst removed one year previously; no complication had occurred at the time. The patient had a past history of asthma, easily treated by salbutamol spray. All went well until the first cyst was manipulated: the ventilating pressures rose, and wheezing rhonchi appeared in both lung fields. This bronchospasm was resistant to an increase in anaesthetic depth, to salbutamol, terbutaline, steroids and 3% halothane for 15 min. It however disappeared completely as soon as the cyst was removed. There were no other signs of an anaphylactic reaction. The same thing occurred during the removal of the second cyst. Postoperative investigations showed the patient to be sensitized to house dust and mites. His asthma is confirmed. Allergologic tests showed no reaction with the anaesthetic drugs used, but a hypersensitivity to the echinococcal antigens. The bronchospasm was probably due to the increased bronchial sensitivity of this patient.