The deformation behavior of polysynthetically twinned (PST) crystals of TiAl alloyed with V and Zr has been studied at room temperature both in compression and in tension as a function of the angle (phi) between the lamellar boundaries and loading axis. The yield stress as well as tensile elongation strongly depends on the angle phi. When compared to binary PST crystals, both V- and Zr-alloyed PST crystals, in particular, Zr-alloyed ones show high yield stress for all orientations. Environmental loss in ductility of TiAl PST crystals is reduced by the addition of V without affecting their intrinsic ductility. Deformation structures of the two ternary TiAl PST crystals have been investigated by transmission electron microscopy. In addition to deformation twins and ordinary dislocations, numerous superlattice dislocations and faulted dipoles associated with them are observed for both V- and Zr-alloyed TiAl PST crystals. Which of these deformation structure constituents prevails in each of the TiAl domains depends on the crystal orientation of the domain. Based on the results obtained, the effects of V and Zr additions on the strength and ductility of two-phase TiAl alloys are discussed.