Controversy has existed about the relative contributions of subendothelial "fibrinoid" deposits and endothelial cell swelling to the thickened glomerular capillary wall and reduced lumen in preeclampsia. A morphometric analysis of the ultrastructural changes in the glomerulus in preeclampsia showed that subendothelial fibrinoid deposits were a significant feature of biopsies during pregnancy, but were absent in many biopsies in the postpartum period. These deposits disappear progressively in the first week after delivery. Capillary wall changes with reduplication of glomerular capillary walls and mesangial interposition are another prominent feature of preeclampsia. These changes resolve gradually and may present for as long as 18 months. Foam cells in glomeruli are rarely found in biopsies during pregnancy, but appear during resorption of the subendothelial deposits in the postpartum period. Electron-dense droplets in glomerular epithelial cells are a characteristic feature of preeclampsia. Immunogold labeling demonstrates that they contain albumen, immunoglobulins, fibrinogen, and complement. Fibrinogen is usually present in an inner electron-dense core in a droplet. IgM is usually in a relatively translucent outer part of the droplet. Other proteins are diffusely distributed. Segmental hyalinosis is a change that closely resembles the changes of preeclampsia, and segmental lesions may appear during preeclampsia and disappear after pregnancy.