We report two sisters who both have had severe attacks of urticaria and angioedema only when taking the contraceptive pill and during the latter half of pregnancy. Although they exhibited many features in common with hereditary angioedema (HAO), the C1 esterase inhibitor levels and other complement components were consistently normal, including levels measured during pregnancy and at the height of the eruption after oestrogen challenge. Aetiological factors in relation to other patterns and causes of urticaria are discussed.