Antagglutinin, a specific protein synthesized by the boar epididymis, was secreted by the principal cells of the initial segment, the caput and the corpus, but was not detectable in the caudal cells. Castration completely abolished the synthesis and secretion of antagglutinin in all epididymal cells. Androgen replacement suggests that the epithelial cells from different segments have differential regulatory mechanisms. The proximal zone appeared refractory to exogenous testosterone; the median zone was a typical androgen-dependent region; and the caudal cells, where an unusual secretion of antagglutinin was detected, revealed still a different reaction pattern. It is postulated that these latter cells depend not solely on androgen but also or exclusively on other factors. Our results, which demonstrate a primary role of the Golgi complex in the secretory process in the epididymal cells, also suggest that the apical smooth endoplasmic reticulum may be implicated in the intracellular transport of glycoproteins to the cell surface.