An amperometric immunoassay technique utilizing a highly dispersed immunoelectrode was developed. The assay method is based on the ‘sandwich’ scheme of immunointeraction. Rabbit IgG has been used as model analyte. Horseradish peroxidase labelled conjugates were employed coupled with amperometric detection of iodine reduction. Highly dispersed ULTI carbon serves as an immunosorbent and at the same time as an electrode material. It was found that the dependence of immunoelectrode response on the time of incubation during the second stage of ‘sandwich’ -based assay was complex. This is probably due to non-equilibrium immuno-agglomeration of sub-micron sized particles of immunosorbent. The improvement in the sensitivity of immunoelectrode by increasing the amount of immunosorbent was demonstrated. The increase in the magnitude of the immunoelectrode response is proportional to the increase of the amount of immunosorbent. A detection limit of 10 pM has been achieved with an overall assay time of less than 20 minutes.