Structural and metabolic statuses of erythrocytes were evaluated using cytophoto- and interferometry, fine-layer chromatography, scanning and transmission electron microscopy, electrophoresis and fluorescent probing in 48 stomach cancer patients. Structural and metabolic disorders were detected in mature erythrocytes in patients with and without anemia. Changes in the structure and metabolism of peripheral blood erythrocytes taking place prior to quantitative changes were identified. Anemia development pathways were dependent on enhanced hemolysis of circulating erythrocytes and influx of immature cells from the bone marrow. The changing statuses of the membranes and metabolism appeared to play quite a role in erythrons being damaged by tumor process. Dysfunctional erythrocytes of stomach cancer patients need to be corrected by membrane-stabilizing and -repairing drugs.