AbstractPolyionenes have been shown recently (A. Rembaum,Appl. Polym. Symp. No. 22, 299, 1973) to produce the following biological effects: (1) bactericidal action, (2) formation of insoluble complexes with DNA and heparin, (3) neuromuscular blocking action, (4) cell aggregation and lysis, and (5) cell adhesion.In the present study, polyionenes of various structures (mainly I3,3, I6,10) were used as molecular probes to gain an understanding of the cell surface phenomena of adhesion on glass‐ and polyionenes‐treated surfaces. Since tumor cells show different surface cell properties, including an increase in the anodic mobility, they bind preferentially to polyionene‐treated surfaces. Normal human diploid WI‐38 cells were found to adhere at a lower rate than SV‐transformed WI‐38 cells. However, cell spreading was accelerated in both cases.A study of the interaction of polyionenes in solutionin vitroandin vivoand polyionenes covalently bound to polymeric microspheres with leukemic murine EL 4 cells and normal thymocytes showed specific cytotoxity towards the leu