Аннотация:The effect of some components of the medium on the growth of Mycobacterium cyaneum B-646 and on the biosynthesis of an exoglycan by the culture was studied. A medium in which the M. cyaneum M variant produced up to 2.2 g of the exopolysaccharide per litre, which was nearly 4 times more than in the original medium, was proposed. The new medium differed from the original one in an elevated content of carbon, iron and potassium (11.2, 5.0 and 1.4 times, respectively) and in a lower phosphorus content (6.7 times). The exopolysaccharide produced by the culture in this medium contained glucose, galactose, fucose and uronic acid. Therefore, its monomeric composition did not depend on the medium used for growing the culture which produced the exopolysaccharide.