Rabbit aortas were examined by light, scanning, and transmission electron microscopy to observe the morphological steps in focal endothelial cell desquamation. The aortas were not subjected to any instrumentation prior to fixation by either immersion alone or combined perfusion and immersion. In areas where boundary layer separation of flow with eddy formation is known to occur, many elongated protruding cells were observed, some obviously partly loosened from the basement membrane. Some of the latter cells appeared to be attached by two ends and to be twisted longitudinally. Single cells, or even sheets of cells, were completely detached. The breaks seemed to have taken place close to, and parallel with, intercellular junctions, but not within these structures. Platelets had reacted both with injured cells and the denuded intimal surface. Thus, the sequence appears to be protrusion of cell body, partial loosening of cells from the basement membrane, breaks near the intercellular junctions, twisting of cells, and complete detachment.