More industrial and commercial value is placed on milk protein concentration but only a little is known about nutritional management of milk protein synthesis in dairy cows (DePeters and Cant, 1992). Some studies on this subject have shown a small positive effect of feed energy on milk protein concentration (Sutton, 1989). However, increase in milk production from the supply of dietary crude protein (CP) could be influenced by the supply and absorption from the small intestine of essential amino acids (AA), and this could be a nutritional betterment if it would protect from rumen fermentation process. Since dietary supply of AA some times gaves poor results it is still puzzling whether production is limited by specific AA or depends on bacterial and protozoon's proteins (BCP) supply to the small intestine. The objective of this study was to examine the effect of dietary CP levels and abomasal infusion of AA on milk yield and composition and to examine if these are key factors in regulating milk protein synthesis.