Blood samples were obtained for serum lipid and oestradiol measurement from 365 women between 7 to 41 weeks of normal pregnancy. In an additional 21 women serum lipid and oestradiol were measured at 20 to 23 weeks gestation and again at 30 to 33 weeks. Significant correlations were noted between changes in the serum triglyceride and oestradiol levels (P less than 0.001) and between changes in serum cholesterol and oestradiol levels (P less than 0.05). The changes in phospholipid and oestradiol levels were not significantly correlated (P less than 0.1). The serum triglyceride level (mean +/- SEM) was highest at 37 weeks gestation (3.8 +/- 0.3 mmol/l), an increase of 400 per cent over the level at 7 weeks. The serum phospholipid level increased by 108 per cent to its highest levels (5.0 +/- 0.2 mmol/l) at 38 weeks and the cholesterol level increased by 93 per cent to its peak (8.7 +/- 0.3 mmol/l) at 38 weeks.