Purpose clusterin in mammalian semen is a secretory form of clusterin (sCLU) with the heterodimeric structure.It is secreted by the epididymis and seminal vesicle.It is generally agreed that clusterin mainly exists on the surface of abnormal spermatozoa and is implicated in decreased sperm motility, sperm aggregation and infertility.However, few studies observe clusterin in normal spermatozoa, which is presumed to be a novel form.Up to now, the systematical information about the presence,localization, origin and function of clusterin in normal human spermatozoa has yet not been established.The aim of our current study is to systematically research clusterin in normal human spermatozoa.