Pulmonary endothelial cells possess a variety of enzymes on their surface. However, the topographical distribution of these enzymes is not known. In this report we describe a simple technique for the preparation of surface replicas of pulmonary endothelial cells using an unmodified critical point drying apparatus and a high vacuum freeze-etch unit. The technique should be applicable for use with all cells in monolayer culture. Endothelial cells grown on glass slides or coverslips were washed thoroughly, fixed and dehydrated. The monolayers were then critical point dried. Surface replicas were prepared in a Balzer's freeze-etch unit. The advantages of surface replicas are that they can be examined with the resolving power of the transmission electron microscope and can be used to examine whole cells. The potential for the surface replica technique may lie in mapping specific enzymes, receptors and cell surface factors. Therefore, to provide a basis for such studies, we have described the appearance of pulmonary endothelial cells in surface replicas.