In this review proteolytic enzymes of starter microflora involved in cheese ripening are described. The best known system is the proteolytic system of primary starter represented by mesophilic and thermophilic lactic acid bacteria. An important role in the ripening of some kind of cheeses is played by enzymes of secondary starter represented by propionic acid bacteria, Brevibacterium linens and some strains of fungi of Penicillium genus. The extent of proteolysis and flavour development in cheese depends on the activity and specificity of all these proteases.