Scanning electron microscopic studies revealed that ascites Dalton's lymphoma cells are distributed singly (25-30%) or in groups of 2-3 cells (55-60%) and 5 or more cells (10-15%) connected together. The percentage of single cells and groups of 2-3 or more cells changes with tumor growth. The number of single cells is maximal 72 h after tumor transplantation. Control tumor cells revealed the presence of blebs--ruffles all over the cells. Cisplatin treatment of the cells in vivo brings about definite changes in the arrangement of blebs--ruffles over the cells. At the later stages of cisplatin treatment disintegration and breaking of the plasma membrane occurs, which ultimately results in the lysis of tumor cells.