OBJECTIVE: To compare the metabolic effects of a lipid-lowering diet containing either low erucic rapeseed (canola) oil or olive oil. METHODS: Twenty-two hyperlipidemic patients participated in a cross-over study comprising two consecutive 3.5-week treatment periods. The participants were free-living throughout the study period, visiting the metabolic clinic initially and at the end of each treatment period for weighing and blood sampling. All food was prepared daily and weighed out for each individual appropriate to his/her energy requirement. RESULTS: Total serum cholesterol, low-density lipoprotein and the ratio between low-density and high-density lipoprotein cholesterol decreased to the same extent on the two diets tested, as did the apolipoproteins B, A-I and Lp(a). After adjustment for body weight changes, most of the reported effects remained virtually unaltered. However, there was a slightly greater decrease in low-density lipoprotein cholesterol with the diet containing rapeseed oil (-17%, p < 0.001) than with the olive oil diet (-13%, p < 0.01) with p < 0.04 for the difference between diets. Also, the intravenous glucose tolerance improved to a similar extent on both diets. CONCLUSIONS: The results indicate that lipid-lowering diets containing either rapeseed oil or olive oil have similar effects on serum lipoprotein concentration and glucose tolerance in hyperlipidemic subjects.