Stability of liposomes from total fraction of E. coli lipids was studied by their ability to preserve encapsulated substance under different incubation conditions--+4 degrees C and +37 degrees C for some concentrations of CaCl2. Two types of vesicules were used: small ones obtained by ultrasonic treatment and larger ones obtained after successive treatment of lipid suspension with Ca2+ ions and EDTA. It has been shown by spectrofluorimetry and radioisotope probe that for both studied types of liposomes their stability decreases with an increase of CaCl2 concentration and rise of temperature. The effect similar to Ca2+ was produced by Mg+2 ions, but not by Na+ ions. Large liposomes are significantly less stable formations than the small ones. Ca+2 ions were shown to induce at first liposome aggregation and then their destruction. Possible action mechanism of metal ions of the second group on liposome stability, the pattern of initiated membrane disturbances and application of these structures as agents during transfer of biologically active compounds in the cells are discussed.