The effect of dietary alpha-linolenic acid (linseed oil) or eicosapentaenoic acid (fish oil) on serum and liver triacylglycerol levels in rats fed diets rich in saturated fatty acids (hydrogenated beef tallow) versus high in linoleic acid (safflower oil) was examined. Feeding fish oil with hydrogenated tallow lowered the serum triacylglycerol concentration while the combination of fish oil and safflower oil failed to do so. Inclusion of fish oil in the hydrogenated tallow diet lowered the triacylglycerol constant in level tissue whereas inclusion of linseed oil had no significant effect. Feeding of linseed oil or fish oil in the safflower oil diet resulted in lowering of the liver triacylglycerol levels. These results suggest that dietary fish oil may have greater hypotriglyceridemic effects in individuals/populations eating diets high in saturated fats compared with those consuming mainly polyunsaturated vegetable oils rich in n - 6 fatty acids.