We have studied 55 samples of amniotic fluid taken by amniocentesis from 32 women, most of whom had arterial hypertension, with or without intra-uterine growth retardation; with or without uncertainty as to their dates. Fetal pulmonary maturity was estimated by determining the lecithin/sphingomyelin (L/S) ratio and the levels of phosphatidylglycerol (PG) in 55 samples. The semi-quantitative levels of PG were worked out using a simple and rapid immunological method. Our results show that there is a good correlation between the two tests. The level of PG is, however, more specific than the L/S ratio, for which we found some false negatives. In particular, there were 7 samples looked at 48 hours before delivery which showed an L/S ratio lower than 2 and a PG at or above 2 micrograms/ml. None of these 7 had hyaline membrane disease. Furthermore the simplicity and speed of this test make it possible to use it routinely.