The effects of 1,25-dihydroxyvitamin D_3 on PHA-and alloantigen-induced human peripher-al blood lymphocyte proliferation,expressions of IL-2R and TfR were investigated by ~3H-TdRincorporation and indirect immunofluorescence methods respectively,The results demonstratedthat 1,25— (OH)_2D_3 had an inhibitory effect on PHA-induced proliferation (IC_(50)=19.1nM),which could partially reversed by exogenous recombinant IL-2,1,25 (OH)_3D_3 at high doses(10-100nM) it had an inhibitory effect.In both PHA-stimulated and alloactivated lymphocytes1,25(OH)_2D_3 could inhibit the expression of TfR and had no effect on that of IL-2R.This studysuggests that 1,25 (OH)_2D_3 in an important immunoregulatory hormone,the properties of whichneed further clarification.