Abstract The diffusion of cadmium in both single-crystal and polycrystalline indium antimonide has been studied using radio-tracer techniques. For the single-crystal material the diffusion was found to obey Kick's law. The diffusivity varied with temperature according to the relation D(T) = D 0 exp(-( Q kT )) . The value of D 0 found was 1 × 10 -9 cm 2/sec, the activation energy Q was 0·52 electron volts. In the polycrystalline material the diffusion followed the relation expected for grain boundary diffusion.