The possibilities of influencing microbial growth and the efficiency of microbial protein synthesis are reviewed. The authors present a detailed discussion of the effects exerted by the level of feed intake, the feeding frequency, the concentrate to forage ratio, the quality of the carbohydrate and protein source, and the interaction of carbohydrate and protein on microbial protein synthesis and, consequently, on the flow of microbial protein. An in-depth knowledge of the above factors influencing bacterial growth and microbial fermentation is essential for the well-balanced feeding of ruminants (primarily dairy cows) of high production level.