Three experiments were carried out on four rams of 40±5 kg body weight fitted with rumen and duodenum cannulas in a 4 x 4 Latin square design. The animals were fed a 1200 g daily basal ration consisting of meadow hay and concentrate (60:40) in two equal portions at 08.00 and 18.00 h. The basal diet was supplemented with rape seed oil, hydrogenated rape seed oil or linseed oil in respective experiments in amounts equal to 0, 4, 8 or 10% dry matter of the diet. Duodenal digesta was analyzed for fatty acid content. Fat addition, independent of the amount of vegetable fat, decreased the polyunsaturated fatty acid level but increased that of monounsaturated fatty acids, consequently causing an increase in the sum of poly- and monounsaturated fatty acids in the duodenal digesta.