Adiponectin is an adipocyte hormone, with relevant roles in lipid metabolism and glucose homeostasis, recently involved in the control of different endocrine organs, such as the placenta, pituitary and, likely, the ovary. However, whether as described previously for other adipokines, such as leptin and resistin, adiponectin is expressed and/or conducts biological actions in the male gonad remains unexplored. In this study, we provide compelling evidence for the expression, putative hormonal regulation and direct effects of adiponectin in the rat testis. Testicular expression of adiponectin was demonstrated along postnatal development, with a distinctive pattern of RNA transcripts and discernible protein levels that appeared mostly located at interstitial Leydig cells. Testicular levels of adiponectin mRNA were marginally regulated by pituitary gonadotropins, but overtly modulated by metabolic signals, such as glucocorticoids, thyroxine and PPAR-, whose effects were partially different from those on circulating levels of adiponectin. In addition, expression of the genes encoding adiponectin receptor 1 (AdipoR1) and AdipoR2 was detected in the rat testis, with developmental changes and gonadotropin regulation for AdipoR2 mRNA, and prominent levels of AdipoR1 in seminiferous tubules. Moreover, recombinant adiponectin significantly inhibited basal and human CG-stimulated testosterone secretion ex vivo, while it failed to change relative levels of several Sertoli cell-expressed mRNAs, such as stem cell factor and anti-müllerian hormone. In sum, our data are the first to document the expression, regulation and functional role of adiponectin in the rat testis. Taken together with its recently reported expression in the ovary and its effects on luteinizing hormone secretion and ovarian steroidogenesis, these results further substantiate a multi-faceted role of adiponectin in the control of the reproductive axis, which might operate as endocrine integrator linking metabolism and gonadal function.