In two cases of Madelung lipoma DNA and RNA synthesis in the material removed at operation was studied by electron-radioautographic techniques. Lipoma adipocytes were found to differ normal ones by incompleteness of the differentiation process. This is manifested by the retention of DNA and RNA synthesis in lipoma adipocytes. A faster rate of proliferation of stromal-vascular cells of lipoma which may be the source of formation of new adipocytes was observed. Intensified DNA and RNA synthesis in patients with Madelung lipoma was observed not only in the cells of the tumor itself but also in the adjacent fatty tissue.