21st Century Acidophilus Probiotic Blend is a proprietary blend of the most beneficial known strain of Lactobacillus Acidophilus, synergistically combined with three other genetically distinct probiotic organisms and prebiotic inulin, is designed to aid in the maintenance of probiotic activity in the intestine. Acidophilus Probiotic Blend contains over 1 billion viable cells at the time of manufacture.