A total of 506 amniotic fluid samples from 337 pregnancies was analysed for lecithin/sphingomyelin (L/S) ratio and phosphatidylglycerol. Two-dimensional chromatography on either laboratory-made or commercial thin-layer silica gel plates was required for proper resolution of the phospholipids. The predictive accuracy of the L/S ratio and the phosphatidylglycerol analysis was assessed in 225 patients, 187 of whom had an L/S ratio of 2 or more. In addition to predicting respiratory distress syndrome of the newborn, the phospholipid results predicted the risk of transient tachypnoea, symptomatic pneumothorax and the persistence of fetal circulation. The phosphatidylglycerol results improved the predictive value of both the mature L/S ratio (2 or more) and the non-mature L/S ratio (below 2).