A stable aqueous dispersion which comprises a cationic lipid which is a molecule which comprises a cholesterol-derived lipophilic group, a linker bond which is hydrolyzable by cellular enzymes and relatively resistant to base-catalyzed hydrolysis, a spacer arm and a cationic amino group, and an appropriate co-lipid. The invention also includes the cationic lipids and mammalian plasmid DNA or other cells in admixture with the aqueous dispersion.