Three female patients had serious anaphylactic reactions to sclerotherapy with polidocanol (Aethoxysklerol) within 15 minutes after administration for varicose veins in the legs. Two of them received the drug for the first time. The first patient developed cardiac arrest which was successfully treated. The second patient showed signs of an adult respiratory distress syndrome, while in the third the ECG was compatible with cardiac ischaemia. Recovery was complete and uneventful in all patients. The incidence of allergic reactions to polidocanol has been estimated at 1:10,000. In view of the considerable underreporting of adverse reactions we feel that the frequency of severe anaphylactic reactions to this drug may be underestimated.