The aim of this study was to investigate metabolism of unsaturated fatty acids in ruminants. We focused particularly on the question if there is a selective mobilisation of n-3 fatty acids from adipose tissue during start of lactation, when demands are augmented. 10 Brown Swiss and 14 Holstein Friesian dairy cows form the herd of the ETH Zurich research station were allotted into 4 groups which got an isoenergetic ration with a concentrate containing different amounts of either n-3 fatty acids as linseed or n-6 fatty acids as sunflower seed. The sampling took place from 6 weeks before to 6 weeks after calving. During this time, feed, blood, adipose tissue and milk samples were taken regularly. 2 weeks before calving, intense metabolic measurements were made. This study shows the influence of the dry period feeding on fatty acid pattern of milk. But the effect lasts only for a few days. Hence there seems to be no use feeding n-3 rich concentrates before calving to enrich milk for human consumption. Fatty acid pattern of milk is mainly influenced by the actual diet. The different contents of unsaturated fatty acids in adipose tissue gives evidence for a selective mobilisation of n-3 fatty acids.