Abstract
A new variant of haemoglobin A (Hb A) with a high affinity for oxygen has been found in an English family. Five members are affected and all are polycythaemic. This variant (Hb Heathrow) is the first of this class to be found in this country and has the same electrophoretic mobility as Hb A. It was discovered only by measuring the oxygen affinity of the patients' red cells. This emphasizes the need for measuring the oxygen affinity of haemoglobin in patients with polycythaemia if other clinical and haematological features associated with polycythaemia rubra vera are absent.