Transgenic animals became easy and open for general use as a source of recombinant proteins and essential components like unsaturated fatty acids. That possibility can completely change the life and health of humans. Thanks to genetic engineering, it is possible to increase the level of healthy fatty acids in animal organism, with the help of e.g. stearoyl-CoA desaturase, fat-1 gene. Milk with changed fatty acids composition could be a cure for people with obesity and vascular problems, as also can be an alternative source of long chain polyunsaturated fatty acids for oil-rich fish and fish liver oils. What is more, also natural environment can be saved by those animals.