This paper describes mixed agglutination and serum absorption experiments for the demonstration of A, B, H, M, N, D, C, E, c and e isoantigens in human epidermal cells and cultured cells. It was found that only A, B and H antigens are present on human epidermal cells and that this does not appear to be related to the secretor status of the donor. The same antigens were also examined on six different established human cell strains (HeLa, EE, ERK-1, Maben, Chang conjunctiva, Chang liver), and one established mouse cell strain (L). It was found that the H antigen persists in established human cell cultures. The M antigen which is not seen in normal epithelial cells can be demonstrated on HeLa cells by mixed agglutination reaction and by absorption experiments. Guinea pig antisera against established cell lines of human origin were found to contain a small fraction of agglutinins with H specificity, but no anti-M, anti-N or anti-Rh agglutinins.