A comparative electrochemical study of human immunoglobulins IgG(1) and IgG(3) carried out at a hanging mercury drop electrode shows that mechanisms other than the reduction of interchain disulphide linkages are responsible for the cathodic peaks observed for such proteins. Considering that the nature of the electrochemical process observed for immunoglobulins are poorly defined and not fully understood, a new approach to the electrochemical determination of such proteins, involving the use of 2,4-dinitrophenol (DNP) as a label, has been developed. Dynamic linear ranges of nearly two magnitudes and detection limits below 10(-10) M were achieved.