In the Corynorhinus mexicanus four enzymes related to Reactive Oxygen Species (ROS) modulation are present in the cephalic and caudal region of the epididymides during the progress of the epididymis sperms and their maturation, but interesting to say the activity of the Super Oxide Dismutase (SOD) is not present or perhaps it is inhibited in both epididymal segments in the post testicular phase of the sperm storage function. The SOD is present during the period of maturation and during the transport of the sperms, but it is almost totally inhibited or not present in both epididymal segments during the storage, as well as an absence in the sperm cells SOD activity. It is interesting to observe that the Gamma Glutamyl Transpeptidase (GGT) and Glutathione PeroXidase (GPX) presents a complete pattern contrary to that of the SOD; its activity is low during the period of production and maturation of the epididymal sperms, but present an important activity in both segments of the epididymis during the storage phase. The activity of CATalase (CAT) is preserved relatively high during the whole reproductive cycle indicating its importance in the protection of the spermatic cells against the effect of Hydrogen peroxide (H2O2). However it is important to mention that its activity is significantly higher in the tail of the epididymis during the maturation and particularly during the storage process. In sperm from the cephalic and caudal region, the CAT activity reaches its highest levels at the beginning of September and the lowest at the end of the same month. In the epididiymal fluid the CAT activity shows a similar pattern in the cephalic region from that found for SOD and GGT/GPX in both regions. The redox balance associated with the microenvironment, through which the sperms pass, must be specific and differentially controlled to assure its adequate function