In this study, we investigated inhibitory effects of some metal ions on human erythrocyte glutathione reductase. For this purpose, initially human erythrocyte glutathione reductase was purified 1051-fold in a yield of 41% by using 2, 5-ADP Sepharose 4B affinity gel and Sephadex G-200 gel filtration chromatography. SDS polyacrylamide gel electrophoresis was done in order to control the purification of enzyme. SDS polyacrylamide gel electrophoresis showed a single band for enzyme. A constant temperature (4°C) was maintained during the purification process. Enzyme activity was determined with the Beutler method by using a spectrophotometer at 340 nm. Hg2+, Cd2+, Pb2+, Cu2+, Fe3+ and Al3+ exhibited inhibitory effects on the enzyme in vitro. Ki constants and IC50 values for metal ions were determined by Lineweaver-Burk graphs and plotting activity % vs. [I]. IC50 values of Pb2+, Hg2+, Cu2+, Cd2+ , Fe3+ and Al3+ were 0.011, 0.020, 0.0252, 0.0373, 0.209 and 0.229 mM, and the Ki constants 0.0254±0.0027, 0.0378±0.0043, 0.0409±0.0048, 0.0558±0.0083, 0.403±0.043 and 1.137±0.2 mM, respectively. While Pb2+, Hg2+, Cd2+ and Fe3+ showed competitive inhibition, others displayed noncompetitive inhibition.