In this project we tested the biological relevance of increased circulating leptin and whether pregnancy might permanently alter circulating leptin. We tested the following hypothesis; free leptin is increased in normal pregnancy, free leptin concentration returns to prepregnancy concentration after normal and preeclamptic pregnancy, free leptin concentrations are not different after pregnancy in women who have had normal or preeclamptic pregnancies. These hypothesis were tested by the following specific aims: We measured free and bound leptin in preeclamptic and normal pregnant patients during pregnancy. We measured leptin fractions in nulligravid patients to have a baseline to compare our data during the pregnancy period. Free leptin is increased in obese individuals and it is the fraction which is altered by perturbations (e.g., feeding and fasting) known to alter circulating leptin concentration. During human pregnancy the total concentration of many hormones in blood is increased with minimal changes in the free active hormone because of an increase in binding proteins. We determined that the increased plasma leptin of normal pregnancy and the further increase in preeclampsia are not simply due to this phenomenon. We compared serum leptin concentration in serum samples obtained from 18 nulligravid women. Two ml serum were loaded into a column packed with Sephadex G-100 at 4 C in order to separate free from bound leptin. Leptin concentration in the fractions were assayed by RIA.