Investigations were conducted to assess the effect of duodenal infusions of oleic and linoleic acids both on milk composition and fatty acid patterns of milk fat. The investigations were carried out in two trials, I and II, each with 3 cows, fitted with a ruminai and a duodenal cannula. 56 g of oleic acid (Trial I) and 46 g linoleic acid (Trial II) were infused daily into the duodenum over a period of 7 days, while no application of fatty acids acted as a control in each case. An increase in milk fat content was observed in both trials whereas the content of protein and lactose in milk remained unaffected. In both trials the milk oleic acid and linoleic acid concentrations increased. In trial I C18: 1increased from 14.8 to 18.7%. In trial II C18: 1increased from 2.5to5.8% of total lipids. It was estimated that 84.8% of the infused C18: 1and 86.5% of C18: 1were transferred into milk fat.