The phospholipid composition has been determined for placental microsomes from 11 normal and eight pregnancies complicated by steroid sulphatase deficiency. Phosphatidylcholine, phosphatidylethanolamine and sphingomyelin were found to be the major phospholipids of normal placental microsomes, comprising respectively 41.6 +/- 4.6% (mean +/- SD). 30 +/- 5.7% and 22.5 +/- 4.9% of the total phospholipid content. There was no correlation between the steroid sulphatase activity of the microsomes and the content of any of the three phospholipids. Though their contents were significantly decreased. (P less than 0.001) phosphatidylcholine, phosphatidylethanolamine and sphingomyelin similarly constituted the major portion of the total phospholipids in sulphatase deficient microsomes, representing 36 +/- 4.2%, 34 +/- 6.1% and 22.4 +/- 6.7% respectively. Only the percentage of phosphatidylcholine was significantly different (P less than 0.02) from normal microsomes. The results show that the decreased phospholipid content of steroid sulphatase deficient placental microsomes reflects a lower content of all major classes of phospholipids, particularly phosphatidylcholine.