Oral supplements of live, beneficial intestinal micro-organisms for nutritional health and well-being are known as probiotics. Probiotic dietary lactobacilli colonize the intestinal tract, depending on the specific bacterium-to-host affinity. Bacteria are continually in competition for colonization space. The original bacterial colonies have an advantage over transient bacteria; however, the composition of the intestinal microflora is dynamic and constantly changing. If harmful microorganisms proliferate, the equilibrium is disturbed, and it becomes difficult even for indigenous bacteria to maintain their necessary territory to colonize the intestine. Antibiotics tend to kill off both beneficial and harmful bacteria, and thus may also disturb the normal, healthy balance of intestinal microorganisms. When potent probiotic supplements, such as Bio-Dophilus, are supplied regularly, chances are greatly increased for establishing a healthy population of beneficial intestinal microorganisms. Once established, a normal intestinal microflora rich in lactobacilli creates acidic conditions that are unfavorable for the settlement of pathogenic microorganisms.