Phosphatidylglycerol (PG) is a minor component (1-2%) of most of cell membranes. It can be found at higher concentrations (up to 11% of the total lipid content) in lung surfactant. It s presence in amniotic fluid indicates fetal lung maturity and is the basis of clinical testing for fetal fitness. PG is also used by cells as an intermediate in cardiolipin synthesis. Bacterial membranes contain up to 20% of PG.