Summary It has been shown that in the puerperium the blood plasma lipids of women decrease in value, the greatest decrease being in neutral fat, next phospholipid, and least cholesterol and its esters. When normal lactation was prevented by dryin g up the breasts, the decrease in plasma lipid levels was inhibited, stopped. or reversed. Evidence was obtained that the lipemia of pregnancy tends to disappear in the puerperium independently of the onset of lactation. It was found that in the early puerperium the plasma fatty acids, especially those in combination with phospholipids, become temporarily more saturated, and this occurred whether or not the patients lactated normally. The red blood cells were also found to exhibit temporary increases in their lipid content, in the early puerperium and this likewise resulted independently of the onset of normal lactation. And the sequence of lipid changes in the puerperium was shown to be identical in nature to the sequence in the disappearance of any other lipemia. This information was taken to indicate that the lipemia of pregnancy disappears after delivery independently of the onset of lactation. It was suggested that lactation may probably assist the decline to normal in the value of plasma lipids. When the breasts were dried up, however, bodily function was apparently altered, resulting in the production of a new lipemia.