Background: Mammalian fertilization is preceded by sperm acrosomal exocytosis. Results: The GTPases, dynamin 1 and 2, were identified within the periacrosomal region of the mouse sperm head and shown to participate in a progesterone-induced acrosome reaction. Conclusion: Dynamin forms part of the molecular machinery that underpins acrosomal exocytosis. Significance: These data provide an important mechanistic insight into the molecular basis of the sperm acrosome reaction.