Two approaches to electrochemical immunoassay are reported. The first approach was an indirect method, involving an electroactive, enzyme-catalysed, substrate to product reaction. Conditions were optimised for the amperometric detection of para-aminophenol, the electroactive product of the alkaline phosphatase catalysed hydrolysis of a new substrate, p-aminophenylphosphate, after separation by HPLC. The second approach involved the direct electrochemical detection of an immunoglobulin species, IgG, and the electrochemical monitoring of the immunological interaction. In an attempt to characterise the electrochemical response of such proteins, studies were carried out on the adsorptive stripping voltammetry of the immunoglobulin fragments, F(ab1 )2 and Fab. The globular proteins avidin and streptavidin, were then studied as these were similarly constructed proteins, except avidin had a disulphide bond, and streptavidin has not. The interaction of avidin and streptavidin with biotinylated IgG was also reported as this is an important labelling procedure in immunoassay.