FESEM of MWCNT penetration of alveolar epithelial cells. As shown in this micrograph, MWCNT were rapidly incorporated into the alveolar epithelium. Micrograph shows two MWCNT passing through an alveolar epithelial cell 1 day after aspiration (80 ug dose). The two fibers are running together on the right side of the cell and appear to separate within the cell as they pass out on the left side of the cell. Another MWCNT penetrates the epithelium in the upper right of micrograph.