The erythrocyte deformability of 28 patients with anemia was evaluated with the laser-assisted optical rotational cell analyzer (LORCA), an image analyzer that converts into numerical form the degree of refraction of a laser beam induced by red cells subjected to a range of torsional stresses. The patients were 10 thalassemics, including three with intermediate forms (1 HbC/beta degree, 1 homozygote beta for Orkin's haplotype VI, 1 beta degree/beta delta Sicilian type) and seven heteroygotes for beta Th; six with hereditary spherocytosis (including 2 with structural alteration of the spectrin beta chain); three with type II congenital dyserythropoietic anemia (HEMPAS), two hemizygotes and one heterozygote for G-6PD deficiency, and six with severe hypochromic hyposideremic anemia. Red cell deformability was reduced in intermediate thalassemia, hereditary spherocytosis and HEMPAS, normal in heterozygous beta thalassemia and G-6PD deficiency, and increased in hypochromic hyposideremic anemia. These results show that erythrocyte deformability can be impaired by an Hb chain imbalance, membrane and cyto skeleton structure anomalies and changes in the red cell area/volume ratio.