The Ultimate Probiotic 12/12 contains 12 different species in a single formula designed to more closely approximate the normal composition of intestinal flora. This completely unique formula supports immune system function and a healthy intestinal flora. The twelve-strain blend has a minimum of 12 billion live cells per strain and are guaranteed to the expiration date, not at time of manufacture like many other brands. Only the highest quality, researched human strains are used in this formula.