Abstract Swiss 3T3 cells in culture have recently been shown to incorporate exogenous,[3H]-glycerol-labeled 2-monoacylglycerol into phosphoglycerides. The pathways that form these phosphoglycerides have yet to be characterized in detail, but a monoacylglycerol kinase and a stearoyl-specific transacylase seem to act successively to initiate one of the major pathways that are involved. This pathway is of special interest because its products appear to include sn-1-stearoyl-2-arachidonoyl phosphatidylinositol and sn-1-stearoyl-2-acyl species of phosphatidylethanolamine and phosphatidylserine. These phosphoglyceride species are key components of animal cell membranes that seem not to be formed by the classical pathways that synthesize phosphoglycerides de novo. Their precise function remains to be determined, but phosphoinositides, phosphatidylethanolamine, and phosphatidylserine are known to be present in the cytoplasmic leaflet of the plasma membrane where they contribute to mechanisms of stimulus transduction and serve as binding sites for many intracellular proteins. Therefore, the sn-1-stearoyl-2-acyl phosphoglycerides that the 2-monoacylglycerol incorporation pathway forms may have an important influence on intracellular events.