The effect of capacitative Ca2+ entry on cytosolic free Ca2+ concentration ([Ca2+](c)) was examined in calf pulmonary artery endothelial cells treated with thapsigargin. Restoration of extracellular Ca2+ evoked an overshoot in [Ca2+](c): the intial rate of Ca2+ influx was 12.4 ± 0.5 nM/s as [Ca2+](c) rose monoexponentially (time constant, τ = 36 ± 2 s) to a peak (322 ± 16 nM) before declining to 109 ± 14 nM after 2000 s. Rates of Ca2+ removal from the cytosol were measured throughout the overshoot by recording the monoexponential decrease in [Ca2+](c) after rapid removal of extracellular Ca2+. The time constant for recovery (τ(rec) decreased from 54 ± 4 s when Ca2+ was removed after 10 s to its limiting value of 8.8 ± 1.0 s when it was removed after 2000 s. The time dependence of the changes in τ(rec) indicate that an increase in [Ca2+](c) is followed by a delayed (τ = 408 s) stimulation of Ca2+ removal, which fully reverses (τ ~ 185 s) after Ca2+ entry ceases. Numerical simulation indicated that the changes in Ca2+ removal were largely responsible for the overshooting pattern of [Ca2+](c). Because prolonged (30 min) Ca2+ entry did not increase the total 45Ca2+ content of the cells, an increased rate of Ca2+ extrusion across the plasma membrane most likely mediates the Ca2+ removal, and since it persists in the absence of extracellular Na+, it probably results from stimulation of a plasma membrane Ca2+ pump. We conclude that delayed stimulation of a plasma membrane Ca2+ pump by capacitative Ca2+ entry may protect cells from excessive increases in [Ca2+](c) and contribute to oscillatory changes in [Ca2+](c).