The effects of pH (4.0, 4.5, or 5.0), temperature (T) (30, 35, or 40 degrees C) and dissolved oxygen (DO) (0.2, 2.0, 4.0, or 6.0 mg O-2/L) on hexokinase and invertase formation by yeast were studied. The highest enzyme activities were attained at pH 4.0, DO = 4.0 mg O-2/L, and T = 35 or 40 degrees C.