Cancer-related causes of anaemia include anaemia of chronic disorders, infections, autoimmune haemolysis associated with malignant conditions, bone marrow invasion by the tumour or clonogenic marrow dysfunction, iron, folate, or vitamin B 12 deficiency and bleeding from tumour erosion. Treatment-related anaemia results from chemotherapy, radiotherapy and bone marrow fibrosis. Severe anaemia increases the burden of treatment, contributes to fatigue, reduces the quality of life and may also delay or limit further treatment. Blood transfusion is currently the most common form of treatment and patients rarely require transfusion unless the haemoglobin is less than 8 g/l. It is often difficult to predict which patients will develop anaemia and require treatment, but the proportion of patients receiving transfusions increases markedly if the pre-treatment haemoglobin concentration is below 10 g/dl. Four studies have systematically evaluated the effects of erythropoietin on anaemia in lung cancer patients and each of these trials is likely to contribute information concerning the clinical benefit of erythropoietin in treating or preventing treatment-related or disease-related anaemia. Most of the improvements in quality of life observed with erythropoietin administration occurred with haemoglobin levels between 10 and 12 g/dl, and not with levels between 7 and 10 g/dl, with a plateau effect above 12 g/dl. Consequently, a 'functional' level of haemoglobin that appears to be more important is 12 g/dl, because it may be favourably associated with a significant improvement in fatigue compared with lower haemoglobin levels. This 'functional' level would be in keeping with the body's physiological erythropoietin response.