This paper reviews the history of the development of probiotics and the effect on the human gastrointestinal microecology. Furthermore, the application of probiotics to yogurt, commonly referred to as bio-yogurt and the effectiveness of yogurt as probiotic carrier food are also discussed. The paper also reviews the literature explaining, in essence, the concept of ‘therapeutic minimum ’ levels and the importance of the survival of probiotic microorganisms in food products. The production of bio-yogurt, survival of probiotic species in yogurt during retail storage, technical considerations for incorporating probiotic microorganisms