Some men have been found not to release prolactin at the time of orgasm even with ejaculation, and therefore, their blood plasma levels of prolactin do not increase (Haake et al., 2002). These men do not have a post-orgasmic refractory period and their orgasms are followed by neither detumescence nor hypersensitivity of the glans of the penis. These men are therefore capable of achieving multiple orgasms accompanied by ejaculation (Haake et al., 2002). These findings suggest that the orgasm-induced prolactin release, rather than ejaculation itself, may cause the subsequent refractory period in normal men.