Unstable and equilibrium foam films and foams formed from solutions of sodium dodecyl sulfate and bivalent electrolyte, MgCl2 or MgSO4, are experimentally investigated. It was found that at low ionic strength and low surfactant concentration the films with magnesium ions are more stable than films with sodium ions. At higher surfactant concentration the films containing MgCl2 become stable while the films with MgSO4 remain unstable. The unstable films exhibit at least five types of rupture which are documented by photographs and frequency distribution curves of the film lifetimes. In the case when magnesium ions are present the formation of lenses inside the film was observed; the lenses contribute to a longer lifetime of the films. With the stable films the transition from common to Newton black film occurs at magnesium concentrations between 0.01 and 0.015 M. The results for the stability of single microscopic films are found to correlate with the results for the foam drainage. Copyright 1997 Academic Press. Copyright 1997Academic Press