The significance of electro kinetic properties of tumor cells can not be accurately assessed without also considering cytogenetic variations between cells and differences In their rates of proliferation. The original assumption that elevated charge densities and increased susceptibility to neuraminidase characterizing tumor cells in general, was confirmed mainly by observations of malignant hepatoma cells in the present study. It was also found that the only property common to both leukemic cells and other malignant cells was an increased susceptibility to neuraminidase. The immunological effects of host animals to the electrophoretic mobility in the transplantable tumor cells were also analysed.