Incubation of Micrococcus lysodeikticus protoplasts with rabbit immunoglobulins containing antibodies against micrococcal membranes and a subsequent two-dimensional immunoelectrophoresis of solubilized membrane antigens allowed to reveal four main antigens of the outer membrane, of which only two are accessible to trypsin attack. The outer antigens disappear after protoplast treatment with snail digestive juice (active substance - phospholipase) and after incubation of growing cells with cerulenin, the inhibitor of fatty acid biosynthesis. Electrophoresis of the "cerulenin" membrane proteins in the presence of SDS revealed the disappearance of five proteins with molecular weights of 120 000, 150 000, 100 000, 68 000 and 16 000. Goat antibodies against rabbit serum or Staphylococcus aureus Cowan I cells (binding IgG gamma-globulins for fragment Fc) being added to the solubilized micrococcal membranes from protoplasts pretreated with antimembrane rabbit gamma-globulins precipitate about 5% of membrane protein. This suggests that the membrane outer layer antigens make up to about 5% of total protein content. The distribution of the components between the outer and inner membrane layers is discussed.