A sperm-specific phospholipase (PL) C, termed PLCζ, is proposed to be the soluble sperm factor that induces Ca2 oscillations in mammalian eggs and, thus, initiates egg activation in vivo. We report that sperm from transgenic mice expressing short hairpin RNAs targeting PLCζ mRNA have reduced amounts of PLCζ protein. Sperm derived from these transgenic mice trigger patterns of Ca2 oscillations following fertilization in vitro that terminate prematurely. Consistent with the perturbation in patterns of Ca2 oscillations is the finding that mating of transgenic founder males to females results in lower rates of egg activation and no transgenic offspring. These data strongly suggest that PLCζ is the physiological trigger of Ca2 oscillations required for activation of development.