FESEM examination of lungs. A high magnification image of MWCNTs on the alveolar epithelial surface is shown in Figure 1A. Arrows indicate numerous points where the MWCNTs are being enveloped by the Type I alveolar epithelium 1 hour after aspiration. Figure 1B shows MWCNTs in the mucous blanket of an airway 1 hour after aspiration. A MWCNT-loaded alveolar macrophage (Mac) is shown passing through the alveolar wall in Figure 1C (28 days post-aspiration, 80 ug dose). MWCNTs penetrating through the endothelial wall into the lumen of a pulmonary venule are indicated by the arrows of Figure 1D (28 days post-aspiration, 80 ug dose).