In the lamellar form of the ordered intermetallic TiAl, mismatches at the lamellar interfaces, of order 1%, give rise to internal stresses and lo interracial dislocations. The geometry of the microstructure ensures extreme plastic anisotropy. Three main trends are evident in the plastic tensile properties: Both the yield and fracture stresses are low when deformation occurs in the plane of the lamellae and they are high when deformation occurs across the lamellae, the ductility is high when the tensile axis lies close to the lamellar plane and low when the tensile axis is nearly normal to the lamellar plane. The variations of the yield stress and the fracture stress are explained principally by the effects of Schmid factors and anisotropies in the Hall-Petch (or Stroh) stresses resulting from the lamellar shapes. The variation in ductility may be understood in terms of a competition between the ductile propagation of dislocations across interfaces and the creation of Stroh cracks at the heads of dislocation pile-ups.