Outer and cytoplasmic membranes of Pseudomonas pertucinogena ATCC 190 and 6627 were separated, and their lipids were analyzed. In the two strains, phosphatidylethanolamine was dominant in the cytoplasmic membrane, but cardiolipin and phosphatidylglycerol were dominant in the outer membrane. Various kinds of fatty acids, namely, odd- and evennumbered, saturated and unsaturated, branched, and cyclopropanoic acids were contained in these strains. Only in strain 190 were unsaturated fatty acids increased in the cytoplasmic membrane, but saturated fatty acids were increased in the outer membrane. Fatty acid distribution to the outer and cytoplasmic membranes in strain 6627 was similar. In the two strains, lysocardiolipin appeared from the early exponential phase of growth and was present at a level eight times higher in the cytoplasmic membrane than in the outer membrane, although phospholipase A activity was located mainly in the outer membrane. From these results, the possibility of the presence of lysocardiolipin as a normal phospholipid constituent of the membrane was discussed. [ABSTRACT FROM AUTHOR]