A membrane enzyme preparation from Streptococcus sanguis was shown to convert sn-[14C]glycerol 3-phosphate and CDP-diacylglycerol (or deoxyCDP-diacylglycerol) into a series of progressively higher-molecular-weight [14C]oligophosphoglycerophospholipids in vitro. The first oligophosphoglycerophospholipid to accumulate (termed lipid-1) was purified to homogeneity; chemical analysis, gas-liquid chromatography and chemical degradation studies indicated the most likely structure to be phosphatidylglycerophosphoglycerol (PGpG). PGpG is formed directly from two molecules of phosphatidylglycerol (PG), one molecule of PG serving as a sn-glycerol 1-phosphate (pG) donor and the second serving as the pG acceptor, with co-production of diacylglycerol. These oligophosphoglycerophospholipids may be intermediates in the biosynthesis of lipoteichoic acids.