The role of calcium in pollen tube tip growth is reviewed. Calcium ions are essential for growth, but are inhibitory at high concentrations (above c. 10-2 M). Calcium intake is limited to the growing tip, and the inward flux of calcium appears to establish an ionic current within the surrounding medium. Cellular transport of calcium is reviewed against a background of the functional requirements for calcium ions. It is concluded that calcium-induced polarized tip growth depends on a dual control system; (1) intake through spatially localized calcium ion channels coupled with (2) cytoplasmic sequestration and transport from the tip region in organelles. This system maintains conditions appropriate for directed activity of the cytoskeleton and subsequent vesicle fusion at the growing tip.