The sexual behaviour of adult male rats was studied following the injection of cadmium chloride in a dose known to induce complete testicular necrosis and permanent sterility. During the first 3 weeks after cadmium injection, most males lost their copulatory activity. This effect could be prevented by administration of androgens. Complete mounts and a normal ejaculatory behaviour pattern were resumed by all males 2 months after cadmium injection. Spontaneous restitution of copulatory activity depended on the presence of the damaged testes. A comparison of the quantitative characteristics of copulatory performance before, and more than 2 months after, cadmium revealed only slight impairment of sexual behaviour.