Dear Editor,rnThe cytosolic protein Tau is naturally present in human neurons,where it has a pivotal role in controlling microtubule stability.1 Hyperphosphorylation of Tau (observed during neurodegenerative diseases,such as Alzheimer\'s disease) impairs the protein\'s ability to bind microtubules.This results in microtubule disassembly and the formation of Tau aggregates2,3 Tau protein is also widely expressed in peripheral tissues.4 In the male reproductive system,screening for Tau has focused solely on the rodent and bovine testis.4,5 In the present study,we used immunofluorescence and immunoenzymatic techniques (with a Tau-specific antibody)6 to investigate the presence of Tau protein in human ejaculated sperm and testicular tissue.We studied (i) five semen samples from normozoospermic men and (ii) testicular biopsies taken from two men suffering from obstructive azoospermia (in whom spermatogenesis was normal).The men were recruited by our university hospital\'s andrology clinic,and all provided their written,informed consent to participation.Briefly,washed,smeared sperm samples were incubated with normal goat serum and then with rabbit anti-C-terminus Tau antibody raised against synthetic peptides encoding the last 15 amino acids of Tau protein (dilution:1∶1000).The slides were revealed with Alexa 488-conjugated goat anti-rabbit antibodies (Molecular Probes(R),Invitrogen SARL,Cergy Pontoise,France).Dewaxed 5 μm paraffin sections were microwaved and incubated with normal sheep or goat serum and then with rabbit anti-C-terminus Tau antibody (dilution:1∶1000).In immunoenzymatic experiments,the sections were revealed with a biotinylated sheep anti-rabbit immunoglobulin G (dilution:1∶150) and then an avidin/biotinylated horseradish peroxidase complex (both from Vector Laboratories,AbCys,Paris,France).