Spermatogenesis is a sophisticated process facilitating transmission of the genetic patrimony and, thus, perpetuation of the species. Mammalian spermatogenesis is classically divided into three 3 phases. In the first--the proliferative or mitotic phase--primitive germ cells or spermatogonia undergo a series of mitotic divisions. In the second--the meiotic phase--the spermatocytes undergo two consecutive divisions to produce the haploid spermatids. In the third--spermiogenesis--spermatids differentiate into spermatozoa. The entire process is regulated by paracrine, autocrine and endocrine pathways, an array of structural elements and chemical factors modulating somatic and germ cell activity (for reviews, see refs. 1-4). The communication network linking the various cellular activities during spermatogenesis is highly complex and sophisticated.