Thus far, the methods used to determine erythrocyte Ca2+influx have not allowed the assessment of the kinetics of ion uptake. To overcome this drawback, we studied a new method, using the fluorescent Ca2+-chelator fura-2, which directly quantifies intracellular Ca2+changes in human erythrocytes. This method has the advantage over previous techniques that it monitors continuously cellular Ca2+levels. The Ca2+influx is modulated by cellular membrane potential in the presence of a transmembrane Ca2+concentration gradient and exhibits a first slow increase of the intracellular Ca2+concentration, followed, after the reachment of a threshold value of 125 ± 13 nM Ca2+, by a faster increase until a plateau is reached. The influx rate is inhibited by dihydropyridines in the micromolar range. These findings support the hypothesis that erythrocyte Ca2+influx is mediated by a carrier similar to the slow Ca2+channels and is dependent on membrane depolarization.