The blood films of patients with sickle cell-haemoglobin C disease (SC) were compared with those of patients with related haemoglobinopathies in order to establish the most characteristic features. The blood films from SC patients generally permitted the distinction from sickle cell anaemia (SS) but not necessarily from haemoglobin C disease (CC) or C/beta thalassaemia. About half of the SC films showed characteristic SC poikilocytes and a minority also had some cells containing haemoglobin C crystals. In addition, SC differed from SS in having fewer classical sickle cells and nucleated red cells, more irregularly-contracted cells and less polychromasia and evidence of hyposplenism.