The expression of recombinant proteins in the mammary glands of trangenic livestock has become an important strategy for the large-scale production of protein therapeutics. Despite the commercial success of this technology, other collectible body fluids are being investigated for recombinant protein production. In this issue, Dyck et al. demonstrate the feasibility of producing proteins in the male ejaculate by expressing human growth hormone in the seminal vesicles of transgenic mice (see p. 1087).