The temperature effect on slip and deformation twinning has been investigated in Cd single-crystals in tension in the temperature range from room temperature to 500 K. The observations of traces on the surfaces of the crystals show that there are twinning and slip at room temperature. Above 430 K slip takes place on the limited slip plane. On the other hand, as the temperature increases deformation twinning occurs on some new twinning plane after considerable slip, although deformation twinning is-a common low temperature mode of-plastic deformation. It is shown that the multiplicity of twinning systems aids deformation by twin rather than by slip in Cd single-crystals at high temperatures.