Bacteria producing bacteriocins have to be protected from being killed by themselves. This mechanism of self-protection or immunity is especially important if the bacteriocin does not need a specific receptor for its action, as is the case for the type A lantibiotics forming pores in the cytoplasmic membrane. At least two different systems of immunity have evolved in this group of bacteriocins containing modified amino acids as a result of posttranslational modification. The immunity mechanism of Pep5 in Staphylococcus epidermidis is based on inhibition of pore formation by a small 69-amino acid protein weakly associated with the outer surface of the cytoplasmic membrane. In Lactococcus lactis and Bacillus subtilis the putative immunity lipoproteins NisI and SpaI, respectively, are also located at the outer surface of the cytoplasmic membrane, suggesting that a similar mechanism might be utilized by the producers of nisin and subtilin. In addition an ABC-transport system consisting of two membrane proteins, (NisEG, SpaG and the hydrophobic domain of SpaF, and EpiEG) and a cytoplasmic protein (NisF, the cytoplasmic domain of SpaF, and EpiF) play a role in immunity of nisin, subtilin and epidermin by import, export or inhibition of pore formation by the membrane components of the transport systems. Almost nothing is known of the immunity determinants of newly described and other type of lantibiotics.