Taken together, these observations strongly suggest that spermatozoa are acutely modulated by VP, in addition to locally released neurotransmitters, that transport defects due to over- or underexpression of AVPR2 and/or AVPR2 mutation, and that aberrant concentration of VP in semen or the male reproductive tract may contribute to male infertility. This evidence concerns the gene AVPR2 and male infertility.