Hyperactivation, a swimming pattern of mammalian sperm in the oviduct, is essential for fertilization. It is characterized by asymmetrical flagellar beating and an increase of cytoplasmic Ca² . We observed that some mouse sperm swimming in the oviduct produce high-amplitude pro-hook bends (bends in the direction of the hook on the head), whereas other sperm produce high-amplitude anti-hook bends. Switching direction of the major bends could serve to redirect sperm toward oocytes. We hypothesized that different Ca² signaling pathways produce high-amplitude pro-hook and anti-hook bends. In vitro, sperm that hyperactivated during capacitation (because of activation of CATSPER plasma membrane Ca² channels) developed high-amplitude pro-hook bends. The CATSPER activators procaine and 4-aminopyridine (4-AP) also induced high-amplitude pro-hook bends. Thimerosal, which triggers a Ca² release from internal stores, induced high-amplitude anti-hook bends. Activation of CATSPER channels is facilitated by a pH rise, so both Ca² and pH responses to treatments with 4-AP and thimerosal were monitored. Thimerosal triggered a Ca² increase that initiated at the base of the flagellum, whereas 4-AP initiated a rise in the proximal principal piece. Only 4-AP triggered a flagellar pH rise. Proteins were extracted from sperm for examination of phosphorylation patterns induced by Ca² signaling. Procaine and 4-AP induced phosphorylation of proteins on threonine and serine, whereas thimerosal primarily induced dephosphorylation of proteins. Tyrosine phosphorylation was unaffected. We concluded that hyperactivation, which is associated with capacitation, can be modulated by release of Ca² from intracellular stores to reverse the direction of the dominant flagellar bend and, thus, redirect sperm.