Plasma lipids and lipoprotein cholesterol distribution were measured in 60 normal pregnancies studied longitudinally at 12, 20, 28, and 36 weeks of gestation and 3 and 40 days postpartum. Total cholesterol, unesterified cholesterol, phospholipids, triglycerides and cholesterol in low- and very-low-density lipoproteins rose progressively during pregnancy. Maximal values were reached at 36 weeks for total cholesterol, unesterified cholesterol and low-density lipoprotein cholesterol and at partum for triglycerides, very-low-density lipoprotein cholesterol and phospholipids. High-density lipoprotein cholesterol was hardly affected by pregnancy. During the second half of pregnancy and postpartum period, high-density lipoprotein cholesterol was consistently and negatively correlated with triglycerides and very-low-density lipoprotein cholesterol. In each period studied total cholesterol showed very high positive correlation with low-density lipoprotein cholesterol but a weak correlation with high-density lipoprotein cholesterol.