The LA/N-cp rat, when homozygous for the mutant cp gene, is obese and moderately hyperlipidemic. Body weight of homozygotes reaches approximately 950 g compared to 400 g for lean heterozygotes. In adult animals plasma triglycerides are 330 mg/100 ml compared to 40 mg/100 ml, and total cholesterol is 215 mg/100 ml, compared to 80 mg/100 ml in heterozygotes. We have examined the arteries of pressure perfusion fixed animals of 9 months age by scanning electron microscopy. Our technique shows normal endothelium in clear detail with each individual cell and its surface structure well defined. Numerous lesions were found in the arteries, including dead endothelial cells, polygonal cells, varying areas of desquamation with attached blood elements, frank ulcerated lesions and old rechannelized thrombus. The lesions were present in both homozygous cp and heterozygous animals, but were more frequent and severe in homozygous rats. We suggest that this strain of rats may provide a useful, inexpensive model for studies on atherosclerosis.