L-cysteine can be modified onto a silver electrode by covalent binding through the sulphur to give very stable and long-lived chemically modified electrodes(CMEs). Hemoglobin(Hb) exhibits an excellent voltammetric response at the resulting CMEs. Linear sweep voltammetric(LSV) measurements of Hb on the CMEs reveal the existence of a linear relationship between the cathodic peak current and the concentration of Hb in the range of 5 X 10−7- 1 X 10−5mol/L. The detection limit is about 2 X 10−7mol/L. The relative standard deviation of results is 4.5% for 10 successive determinations at 2 X 10−6mol/L. Other proteins and chemicals present in samples do not interfere in the assay.