The aim of this study was to determine whether conjugated alpha -linolenic acids (CLnAs) could inhibit the early stages of atherosclerosis by altering the lipoprotein profiles or preventing the formation of fatty streaks in the aorta. F< sub>1B hamsters were fed a control or one of the 3 hypercholesterolaemic (HC) diets: HC-control, HC-RA (18:2 cis-9, trans-11) or HC-CLnA (CLnA: equimolar mixture of 18:3 cis-9, trans-11, cis-15 and cis-9, trans-13, cis-15) diet. In low-cholesterol control-fed hamsters, the proportion of high-density lipoprotein cholesterol (HDL-C) was around 45%, whereas in HC-fed hamsters, HDL-C was around 10% and cholesterol was mostly (80%) carried by triglyceride-rich lipoproteins (TRL). Low-density lipoprotein (LDL) triglycerides (TGs) increased by approximately 60% in hamsters fed either HC-RA or HC-CLnA compared with HC-controls but not compared with the low-cholesterol control diet. HDL cholesterol decreased by 24 and 16% in hamsters fed HC-RA and HC-CLnA, respectively. Small dense LDL-cholesterol increased by approximately 60% in hamsters fed HC-RA and HC-CLnA compared with the HC-control group, and by more than a 100% compared with hamsters fed control diet. The relative percentage of liver cholesteryl ester content increased by 88% in hamsters fed HC diets compared with the control diet. Significant differences in fatty streaks were observed between control and HC-diet-fed hamsters. However, no significant difference was observed among the HC-diet-fed hamsters. This study showed that animals fed any of the HC diets developed an adverse lipoprotein profile compared with a normal lipid diet. Also, HC-RA or HC-CLnA diets altered lipoprotein profile compared with animals fed the HC-control diet, but had no beneficial effects on atherosclerosis.