Estradiol-treated, castrated male rats that had no penile reflexes ex copula (supine position with penile sheath retracted), displayed normal motor patterns of copulation. These males were compared with testosterone-treated castrates for their ability to achieve vaginal penetration. Males were presented with sexually receptive female rats that had been intravaginally injected with nontoxic tempera paint. After each intromissive pattern and ejaculatory pattern the glans penis was inspected for pigment. If the glans was coated, an insertion was assumed to have occurred, and the female was replaced by another female prepared with a different color. Estradiol-treated males typically gained insertion, and their copulatory performance was similar to that of testosterone-treated males. Estradiol-treated males, however, had significantly lower penile weights and bulbocavernosus muscle weights than did testosterone-treated males. Thus, the somatic and neural tissues responsible for sexual reflexes in copula are androgen sensitive, but their function is not androgen dependent.