For two years a 19-year-old patient had been complaining of recurrent abdominal symptoms consisting of severe colicky pain, nausea, vomiting and diarrhoea. Occasionally he noticed concomitant subcutaneous swellings in the limbs. There were no swellings in the face or the region of the upper airway. The symptoms occurred once or twice a month, spontaneously receding within 3-4 days. These signs and symptoms indicated hereditary angio-oedema. Serum concentration of C1-esterase inhibitor was normal (13 mg/dl), but its serum activity was reduced to 16% (normal range 80-125%). This is thus a case of type II C1-esterase inhibitor deficiency. Since starting low-dosage treatment with Danazol (initially, for two months, 200 mg daily, then 200 mg five times per week) the patient has been symptom-free.