Anti-cancer gene therapy should ultimately lead to specific growth inhibition and loss of tumorigenicity of the tumor cells. Therefore, when using cationic liposomes as DNA delivery systems, it is essential to know how the liposome-plasmid DNA complex itself influences the cell growth. This paper reports on the finding that liposome-plasmid DNA complexes specifically inhibited proliferation of human ovarian carcinoma cells, in vitro and in vivo. This inhibiting activity is likely to be sequence independent, since it was observed using several different plasmids. The degree of growth inhibition appeared dependent on both the lipid to DNA ratio and the total dose of liposome-plasmid DNA complex given to the cells.