Monoclonal antibodies (Mab) IKO-21 and IKO-25 obtained to the membrane antigen of the woman milk lipid globules were tested immuno- and cytochemically on the samples of human normal definitive and embryonal tissues and tumours. Mab IKO-21 are shown to react, apart from epithelial tissues, with a vascular endothelium and blood cells. Mab IKO-25 are specific to the epithelial tissue and malignant epithelial tumours. Their intensive reaction with the cells of malignant tumours of the mammary gland, lung, ovary and the type of their distribution in the organs and tissues enables their use in the differential diagnosis of malignant epithelial and non-epithelial tumours as for revealing metastases both in vitro and in vivo.