CD231 (TALLA-1, T-ALL-asociated antigen 1), also known as tetraspanin 7, is a 150 kDa (under reducing conditions 32-45 kDa) transmembrane glycoprotein of tetraspanin family, expressed in T-type acute lymphoblastic leukemia, neuroblastoma, and neuronal tissue. Mutations of CD231 gene are associated with X-linked mental retardation, Huntington´s chorea, and myotonic dystrophy. CD231 interacts with integrins and may have a role in the control of neurite outgrowth. Antibodies to CD231 are important for detection of T-ALL and are potential targets of its treatment.