[en] When injected into the peritoneal cavity, ethidium bromide can strongly inhibit the multiplication of mouse Ehrlich ascites tumour cells. This antitumour effect is increased when ethidium bromide is linked to DNA and also injected into the peritoneal cavity. The cellular alterations are identical after a treatment with E.B. either free or bound to DNA. However, when the cells are treated with E.B.-DNA they contain E.B. for a longer period than after a treatment with E.B.