Fertilization is a fundamental biological process that produces a new and unique individual, enabling species preservation and evolution through sexual reproduction. Sperm cells are uniquely equipped to reach, recognize and fuse with the egg. To perform such diverse tasks, spermatozoa must be prepared to face the challenges presented by their constantly changing surroundings. Thus, sperm cells heavily rely on sophisticated signal transduction mechanisms to swim in a directed fashion, and to adjust to changing environmental conditions. Ion-mediated signal transduction is particularly important in sperm cells, as they essentially lack the protein synthesis capabilities required for signaling mechanisms normally available to other cell types. Accordingly, fluctuations in intracellular Ca2+ concentrations ([Ca2+]i) trigger and/or regulate some of the main sperm functions involved in fertilization. These include motility, capacitation (a process that confers fertilization capability), and the acrosome reaction or AR (a Ca2+-dependent exocytotic event required for fertilization). The extent of participation and the specific roles of the many putative Ca2+ channels thought to mediate sperm functions still remain to be elucidated. Based on studies conducted on various other cell types, Transient Receptor Potential (TRP) channels are known to be a functionally diverse family of Ca2+ channels; they modulate [Ca2+]i in response to various thermal, chemical or mechanical stimuli. Members of the M (Melastatin) subfamily (TRPM) participate in sensory physiology, both at the cell and organismal levels. For example, they are responsible for sensing, among other stimuli, changes in temperature, osmolarity, voltage and/or pH. Importantly, these channels are often sensitive to more than one stimulus and are thus regarded to function as signal integrators. While this particular feature is conceivably of great value for sperm cells embarking on their adventurous journey towards the egg, the involvement of TRPM channels in sperm physiology has not been established. We therefore centered this work on the characterization of TRPM8 -a Ca2+ channel known to open upon temperature decrease- both in mouse (CD-1 strain) and in human sperm. Using specific antibodies, we first show that TRPM8 immunolocalizes to the head and to the flagellum in both species (n=3); the expression of this channel was confirmed by Western blot analyses (n=3) in both species. We then studied the functionality of sperm TRPM8 by: (a) measuring [Ca2+]i using fluorescent dyes; (b) measuring AR induction using standard methodologies for mouse (1) and human (2) sperm; and (c) measuring ion currents making use of the recently established sperm patch clamping technique (3), which is performed on a unique cytoplasmatic extension of sperm cells known as the cytoplasmic droplet. We found that menthol (a TRPM8 agonist) elevates[Ca2+]i inducing the AR in a dose-dependent manner both in human and mouse sperm (IC50 = 300 and 500 µM, respectively). BCTC (N-(4-t-Butylphenyl)-4-(3-Chloropyridin-2-yl) tetrahydropyrazine-1(2H)-carboxamide) and capsazepine (two TRPM8 antagonists) inhibit the menthol-induced AR in both species (n=3). In human sperm these inhibitors did not interfere with the AR induced by two of the physiological inductors, namely ZP3 (zona pellucida protein 3) and progesterone, suggesting that TRPM8 activation triggers the AR through a different signaling pathway than these physiological inductors (2). The effect of low temperature was also tested in mouse sperm, where it induced an increase in [Ca2+]i. However, in this species, BCTC and capsazepine did inhibit -at least partially- the ZP3- and progesterone-induced AR (n=3). Consistently, we found that spermatozoa from TRPM8 knockout mice do not undergo the menthol-induced AR that is sensitive to TRPM8 antagonists (n=3). Patch clamp experiments were exclusively conducted in testicular mouse spermatozoa, revealing currents triggered by menthol, icilin (another TRPM8 agonist), and low temperature. These currents were inhibited by BCTC and capsazepine (n=3), confirming they are due to TRPM8 activity (1). Further studies are needed to elucidate the precise roles that TRPM8 channels may play during fertilization, but the present confirmation of their expression and functionality in sperm cells places them as likely signal integrators in Ca2+-mediated signaling. As such, these channels become attractive subjects of investigation as plausible participants in chemotaxis and thermotaxis -two processes whose involvement in fertilization is still awaiting confirmation.