Abstract A thin-layer Chromatographie method for assay of acetone precipitated phospholipids of amniotic fluid of use in prenatal diagnostics is described. The lipids separated on the chromatoplate were quantitatively assayed by a direct densitometric method, and the phospholipids expressed in proportion to sphin-gomyelin. Blood admixture and activity of lipases in the amniotic fluid will give misleading results. Lipases could be impeded by ethylenediaminetetraacetate. The extraction volume of chloroform—methanol and the evaporation temperature are crucial. Confusion of sphingomyelin and lysophosphatidylcholine could be a source of error.