1. Rates of erythrocyte Ca2+ inward transport, activities of erythrocyte Ca2+-adenosine triphosphatase, Na+, K+ pump, Na+-K+ co-transport and Na+-Li+ exchange, and erythrocyte Ca2+, K+ and Na+ contents have been determined in patients with carcinomas of the head and neck.
2. Decreases in Ca2+ inward transport and Na+-K+ co-transport activity, and increases in erythrocyte Ca2+ and K+ contents, were observed.
3. The more pronounced changes found in advanced carcinoma stages proved to be related to a 50% incidence of a mild anaemia of chronic disease in patients with carcinoma stages T3 and T4.
4. ‘Young’ (light) erythrocytes from healthy donors obtained by density centrifugation showed modifications in Na+ transport and K+ content similar to those seen in the patients.
5. It is concluded that the decrease in Na+-K+ co-transport activity, as well as the elevated K+ content and the lowered mean corpuscular haemoglobin content, but not the disturbances in Ca2+ homoeostasis, in erythrocytes of patients with carcinomas of the head and neck are most probably due to the occurrence of a mild anaemia of chronic disease in advanced carcinoma stages, associated with a reduction in mean erythrocyte age.