alpha-Galactosidase activity in Bifidobacterium longum was maximal in a range of 40-45 degrees C and at pH of 5.8. At temperatures above 60 degrees C the enzyme was completely inactivated, but it maintained a 100% activity during storage at low temperatures (4, -30, -70 degrees C) for 3 months. The addition of Hg2+ to the reaction buffer produced a strong inhibitory effect while Mn2+ exerted a slight positive effect upon activity. The addition of EDTA, inhibitors and other metal ions had no effect on the enzyme alpha-galactosidase.