1. The major free lipids of Corynebacterium aquaticum were characterized as dimannosyl diglyceride, monomannophosphoinositide and phosphatidylethanolamine. Bisphosphatidylglycerol and phosphatidylglycerol were also tentatively identified. 2. We regard this as the only well-documented case of an organism containing monomannophosphoinositide to the exclusion of dimannophosphoinositides and the higher homologues. 3. The co-existence of the two mannolipids in one organism is a distinctive feature. So also is the presence of phosphatidylethanolamine in a corynebacterium. 4. The monomannophosphoinositide apparently does not utilize phosphatidylinositol as a precursor, unlike the monomannophosphoinositide of Propionibacterium shermanii. CDP-diglyceride may be necessary for its synthesis.