The distribution of phospholipids in developing soybean seeds [Glycine max (L.) Merr., var. "Chippewa 64," "Harosoy 63," "Wayne," and "Clark 63"] was followed. From 30 to 60 days after flowering expressed as mole per cent of phospholipid phosphorus phosphatidic acid decreased from 14.8 to 9.1; phosphatidylinositol increased from 0 to 9.1; phosphatidylcholine increased from 8.2 to 9.8; phosphatidylethanolamine increased from 5.3 to 8.6; phosphatidylglycerol increased from 3.2 to 4.8; diphosphatidylglycerol increased from 2.7 to 4.1; and N-acylphosphatidylethanolamine decreased from 65.8 to 54.6. However, from 60 days after flowering to maturity, phosphatidic acid decreased to 0; phosphatidylinositol increased roughly 2-fold; phosphatidylcholine increased roughly 4.7-fold; phosphatidylethanolamine increased 3-fold; N-acylphosphatidylethanolamine decreased 11-fold; whereas phosphatidylglycerol and diphosphatidylglycerol remained essentially constant. Percentages of individual phospholipid species were not statistically different between any two varieties at a given time period.Immature soybean cotyledons incubated with (14)C-acetate or -pyruvate demonstrated rapid incorporation into the phospholipid fraction. N-acylphosphatidylethanolamine was found to account for nearly 70% of the total radioactivity incorporated by the total polar lipid fraction and greater than 30% of the total radioactivity added.