The second messenger cyclic adenosine monophosphate (cAMP) has a central role in sperm physiology. Extracellular cAMP can besequentially degraded into 50AMP and adenosine by ecto-phosphodiesterases (ecto-PDE) and ecto-nucleotidases, a phenomenoncalled extracellular cAMP-adenosine pathway. As cAMP-adenosine pathway is involved in sperm capacitation, we hypothesize thatextracellular PDEs are functionally present in seminal plasma. Exclusively measuring cAMP-PDE activity, total activity in bovineseminal plasma was 10.1 1.5 fmoles/min/lg. Using different family-specific PDE inhibitors, we showed that in seminal plasma,the major cAMP-PDE activity was papaverine sensitive (47.5%). These data support the presence of PDE10 in bovine seminal plasmaand was further confirmed by western blot. In epididymal fluid, total cAMP-PDE activity was 48.2 14.8 fmoles/min/lg and weshowed that the major cAMP-PDE activity was 3-isobutyl-methylxanthine insensitive and thus ascribed to PDE8 family. PDE10AmRNAs were found in the testis, epididymis, and seminal vesicles. cAMP-PDE activity is present in bovine seminal plasma and epi-didymal fluid. The results suggest a role for ecto-PDEs present in those fluids in the signaling pathways involved in sperm functions.