The term probiotics has been defined “living microorganisms, which upon ingestion in certain numbers exert health benefits beyond inherent general nutrition. The original idea with probiotics was to change the composition of the normal intestinal microflora from a potentially harmful composition to a microflora that would be beneficial for the host. In order to function as probiotics, bacteria first must pass through the stomach and survive its low pH and then proceed to the small intestine and tolerate the bile salt present. Finally, it is believed that the bacteria need to adhere to mucosal surfaces. Previously, we discussed the consequences of withdrawal of antibiotics from swine diets and looked carefully at Danish data where this has been done systematically and the consequences documented. From those studies, we could see that antibiotics could indeed be withdrawn from the diets of ALL animals in the production cycle, but when things went wrong the consequences were significant and there was a surge of therapeutic antibiotic usage to suppress the disease situation. The most significant problem is the weanling pig. In order to keep the disease situation suppressed, the management system known as segregated early weaning or medicated early weaning was rapidly established. However, this management system only reduces the likelihood of exposure to pathogenic bacteria and interferes with the establishment of normal protective bacterial flora. This lack of protective bacterial flora has caused an emergence of “new” disease problems in post-weaned pigs such as E. coli diarrhea, edema disease, Glasser’s disease, streptococcal meningitis and Salmonellosis. A study in China on 50-day-old weaned piglets showed that a low dose of probiotics could increase liveweight, reduce diarrhea and lower ammonia odours, so there is good evidence to show that probiotics are effective, however, future issues will address prebiotics, other types of supplements, specialized nutrition and management.