Calcium currents across the plasma membrane of plant cells allow transduction of environmental signals as well as nutritive calcium uptake. Using transgenic Arabidopsis plants with cell-specific expression of green fluorescent protein (GFP), we analyzed whole cell calcium currents in epidermal cells of the rapidly growing root apex, mature epidermal cells, cortical and epidermal cells from the elongation zone, and mature pericycle cells. In cells only from the rapidly growing root apex, a hyperpolarization-activated calcium current was identified. This current was irreversibly inhibited by 10 microM Al3+, as well as being inhibited by 1 mM Co2+ and 100 microM verapamil. In no cells could a depolarisation-activated current be attributed to calcium influx. In the growing root apex, the hyperpolarization-activated calcium current may function to allow constitutive uptake of calcium for rapid cell division and elongation.