30 rats were divided into 3 experimental groups. These included 8 days of Lipofundin treatment + 8 days recovery period (Group I), 16 days of Lipofundin treatment (Group II), and 16 days of Lipofundin treatment + 8 days recovery period (Group III). After sacrifice semi-thin and ultra-thin sections prepared from the aorta segments were examined light and electron microscopically. In addition to the development of alterations characteristic of the Lipofundin-model, the accumulation of collagen fibres was also observed. After 16 days of Lipofundin treatment the alterations were much more advanced than after 8-day treatment. Subsequent migration of smooth muscle cells through the newly formed internal elastic lamina was apparent and led to thickening of the sclerotic plaque. When the 16-day Lipofundin treatment was followed by a recovery period of 8 days prior to sacrifice, no signs of regression were seen. The alterations were present in unchanged form and the only difference was in the extent of accumulation of collagen fibres.