Phosphatidylglycerol (PG) was absent from lung effluent in 41 infants with respiratory distress syndrome of the newborn (RDS), whereas effluent from healthy control subjects of similar gestational age contained this phospholipid (4.9 ± 2.4% of lipid-phosphorus (P),n= 32). Control infants of 28 weeks of gestation or less with various respiratory disturbances other than RDS also had low PG (0.2 ± 0.2% of lipid-P,n= 5). In RDS surfactant complex often could be isolated from the airways using differential and density gradient centrifugation. The material thus obtained had prominent phosphatidylinositol (PI) (13.6 ± 2.8% of lipid-P,n= 6), but no PG. Of those 18 infants who had such surfactant even in the early stages of RDS, 13 were 35 weeks of gestation or more, 3 were offspring of diabetic mothers, and 2 had severe perinatal asphyxia. In healthy control subjects PG sometimes appeared first within an hour of birth, but in RDS PG did not appear until recovery from RDS.In RDS type II (transient tachypnea of the newborn) PG in lung effluent also was abnormally low (1.3 ± 0.6% of lipid-P, n = 5) and PI was correspondingly prominent (9.7 ± 3.6% of lipid-P,n= 5), indicating immaturity of surfactant similar to RDS.Surfactant with PG and PI has superior surface-active properties compared to that containing PI, but no PG. Surfactant without PG does not seem to stabilize the alveoli of the newborn as well as does surfactant with PG. The failure of PG appearance following birth therefore may precipitate RDS, especially beyond 35 weeks of gestation.SpeculationPre- and postnatal monitoring of the acidic phospholipids, PG and PI, in lung effluent is useful in diagnosis and follow-up of RDS as well as in evaluation of various therapies.