In the present study is described an immunoenzymatic assay for a new semi-synthetic immunomodulator consisting of a fraction derived from the strain ATCC 53966 ofCorynebacterium granulosumto which were coupled polyaminoacid chains as a carrier to improve the oral bioavailability of the compound. This assay consists of having the specific antibody reacting with the compound and to determine the amount of antibody that has bound to the compound. For this the bound antibody was first reacted with the corresponding antispecies IgG antibody labelled with an enzyme and then the immobilized labelled antibody was revealed by a colorimetric reaction using a chromogenic substrate. The assay has further been validated by calculating the correlation factor linking the results obtained using the immuno-enzymatic assay to those obtained by determining with the aid of gas chromatography the concentration of muramic acid, a component characteristic of the compound structure.