NOW Foods Acidophilus and Bifidus 8 Billion is a powerful and popular probiotic combination that incorporates three of the most important species of these "friendly bacteria": Lactobacillus acidophilus, Bifidobacterium lactis and Bifidobacterium longum. Multi-species probiotic formulas like this one from NOW Foods are the way to go, since different species have different functions in different parts of the digestive tract. People use NOW Acidophilus and Bifidus during or after intestinal illnesses (like food poisoning, diarrhea, etc) or for general immune support. Keep refrigerated to maintain full potency.