A rabbit antiserum to the meconium antigen of the human fetal intestine is obtained by immunization of rabbits by this substance preparation. The preparation is extracted from meconium by the sulphate ammonium (70% saturation) treatment and gel filtration of supernatant with selection of the 240 kD fractions. In the indirect immunoperoxidase reaction the antiserum reacts with epithelium of certain normal and fetal tissues. It displays oncofetal features in colon, since it reacts with fetal and malignant epithelium and does not react with normal epithelium of this organ. The developed test-system may be used in pathomorphology for the morphological and functional state of colon mucosa evaluation.