The Fura-2 method is used to examine a possible action of 17beta-estradiol (E2) on [Ca2+]i of splenic T cells isolated from female C57BL/10 mice. E2 concentrations between 10 fM and 10 nM induce a rapid and dose-dependent increase in [Ca2+]i due to Ca2+ influx and release of Ca2+ from intracellular stores. Ca2+ influx is mediated by Ca2+ channels which are completely blockable by Ni2+ and partly by nifedipine. The antiestrogen tamoxifen does not inhibit the E2-induced rise in [Ca2+]i. Ca2+ influx and Ca2+ release from intracellular stores is also inducible by plasma membrane impermeable E2 conjugated to BSA. E2-BSA-FITC binds to the surface of T cells of both the CD4+ and CD8+ subset. Our data suggest a novel E2-signalling pathway in T cells which is not mediated through the classical nuclear estrogen receptor response but rather through putative plasma membrane receptors for E2.