Fluid secretion and reabsorption are of central importance in male reproductive (MR) physiology. However, the related molecular mechanisms are poorly known. Here, potential roles for AQP7 and AQP8, two aquaporin water channels abundantly expressed in the MR tract, were investigated by studying their expression and distribution in the developing testis of the Wistar rat. By semiquantitative RT-PCR and immunoblotting, first expression of AQP7 was noted at postnatal day 45 (P45), with levels increasing substantially at P90 and remaining at high levels thereafter. AQP8 began to be expressed at P15, rapidly increased until P20, and remained fairly stable thereafter. Immunohistochemical analyses demonstrated AQP7 in elongated spermatids, testicular spermatozoa, and residual bodies at P45 with increased signal intensity thereafter. AQP8 was observed in primary spermatocytes from P20 to P30 and, in elongated spermatids, residual bodies and Sertoli cells at P30 and thereafter. The ontogeny and distribution of AQP7 and AQP8 in rat testis suggest involvement in major physiologic changes in testis development and spermatogenesis.