We evaluated by means of (1) indirect immunofluorescence and (2) densitometric analysis of stained sodium dodecyl sulfate-polyacrylamide gels the distribution and amount of vimentin and desmin in the aortic media and intima of normal rats and of rats in which the endothelium had been removed by means of an inflated balloon catheter. According to previous reports, in normal aorta vimentin was found in endothelial cells and in the majority of smooth muscle cells, and desmin was found in several smooth muscle cells. Smooth muscle cells present in areas of intimal thickening in rats whose aortas were injured with a balloon were stained only with vimentin antibodies, whereas in the media underlying intimal thickening, the distribution of vimentin and desmin was similar to that seen in normal rats. Portions of aorta (media plus intima) with intimal thickening had a significantly increased vimentin to desmin ratio compared with similar portions of aorta in normal rats. These results suggest that after endothelial injury either only vimentin-containing smooth muscle cells are responsible for replication and migration into the intima, or that smooth muscle cells, while migrating into the intima, synthesize only vimentin.