Apparent hypoxaemia as a result of in-vitro oxygen consumption sometimes occurs in patients with leucocytosis or thrombocytosis (Hess et al. 1979). Among patients with leukaemia, this phenomenon occurs most commonly in acute myeloid leukaemia (Hess et al. 1979). We report the occurrence of an extreme but spurious anoxaemia in a patient with chronic myeloid leukaemia (CML) in chronic phase.