Whether La3+ can enter human peripheral blood lymphocytes by the Na+/Ca2+ exchanger or not and the effect of La3+on the Na+/Ca2+ exchanger activity are examined by fura-2 technique. And that whether La3+ is sequestered by intracellular organelles (mainly endoplasmic reticulum and mitochondria) is studied by this method. La3+uptake is obviously stimulated by pre-treating the cells with ouabain and by removing extracellular Na+, and intracellular La3+concentration ([La3+]i) is directly proportional to its extracellular concentration ([La3+]o). But when [La3+]o exceeds 0.4 mmol/L, the 340/380 nm ratio of fluorescence is no longer varied and the maximum [La3+], is 1.5×10-12 mol · L-1. The higher concentration of La3+ (0.1 mmol/L) increases Na+/Ca2+ exchange-mediated calcium influx, but lower concentration (10 μmol/L) appears to block calcium influx. The results also suggest that cytosolic La3+ is transported by the ATP-dependent Ca2+ pump. Intracellular Ca2+ stores are depleted by ionomycin, and then ion Whether La3 + can enter human peripheral blood lymphocytes by the Na + / Ca2 + exchanger or not and the effect of La3 + on the Na + / Ca2 + exchanger activity were examined by fura-2 technique. And that whether La3 + is sequestered by intracellular organelles (mainly endoplasmic reticulum La3 + uptake is obviously stimulated by pre-treating the cells with ouabain and by removing extracellular Na +, and intracellular La3 + concentration ([La3 +] i) is directly proportional to its extracellular concentration ([La3 + ] o). But when [La3 +] o exceeds 0.4 mmol / L, the 340/380 nm ratio of fluorescence is no longer varied and the maximum [La3 +], is 1.5 × 10-12 mol · L-1. The results also suggest that cytosolic La3 + is transported by ATP-dependent Ca2 + pump. The results also suggest that cytosolic La3 + is transported by ATP-dependent Ca2 + pump. Intracellular Ca2 + stores are depleted by ionom ycin, and then ion