The production of extracellular beta-amylase by some Bacillus cereus, Bacillus megaterium and Bacillus polymyxa [corrected] strains was investigated, and the maximal yields of the enzyme were 3.6; 9.3 and 20.4 U/mL of the culture fluid, respectively (U, 1 mumol of maltose equivalent per min at 30 degrees C). Several cultivation media were used for beta-amylase production. Bacillus cereus and some strains of Bacillus megaterium gave good yields of beta-amylase only in medium with the addition of nutrient broth. However, beta-amylase produced during growth in protein rich medium (nutrient broth) was highly unstable, probably due to inactivation by proteolytic enzymes co-existing in the culture fluid. Bacillus polymyxa [corrected] strains can produce good yields of beta-amylase on a semi-synthetic medium consisting of inorganic salts, potato starch and inexpensive soybean extract instead of costly peptone and meat extract. The most potential beta-amylase producer was the strain Bacillus polymyxa [corrected] NCIB 8524. The tested Bacillus megaterium and Bacillus polymyxa [corrected] strains were apparently differentiated by temperature cultivation (30 and 37 degrees C) suitable for beta-amylase amylase yield.