Cell culture in vitro, ABC-ELISA,RNA dot blot and atom absorption spectrum analysis were used to study biological effects of low concentration of iron citrate (Fe-cit) on the expression of transferrin receptor (TfR) in healthy human peripheral lymphocytes. Results showed that TfR increased by 36%, 50%, and 67% in groups with 1.25 x 10(-5), 5 x 10(-6) Fe-cit and without it, respectively as compared with a control group with 2.5 x 10(-5) mol/L Fe-cit. Levels of TfR-mRNA also increased with decrease of iron in substrate. Iron concentration within cells correlated inversely to the change in the number of TfR. It indicated that iron deficiency could regulate the number of TfR in lymphocytes and its gene expression.