Phytohemagglutinin (PHA) and concanavalin A (Con A) were used as probes to detect changes in the cell surface of Dalton's lymphoma, sarcoma-180 and Ehrlich's carcinoma after short in vitro exposure to acriflavine. Dye-treated cells showed enhancement of agglutination both by PHA and Con A, and such enhancement was found to be dependent on the time of exposure and concentration of acriflavine. However, PHA-induced percent agglutination seemed to be much higher than that of Con A among the 3 cell types. There were also marked differences among the 3 cell types in order of their sensitivity to lectin-mediated agglutination. The strength of the response was greater in lymphoma to both PHA and Con A than that of sarcoma-180 and carcinoma cells, which appeared to be most resistant. Acriflavine, which is known as an intercalative agent with DNA, induces cell surface changes by promoting lectin-mediated cellular agglutination.