The frequent development of allergic respiratory diseases in patients with histories of atopic dermatitis (AD) in early childhood has been known for a long time. At school age, AD has been associated with an increased risk of asthma, and was thus regarded as one of the first steps in a successive "atopic march" leading from AD to asthma. Probiotics are cultures of potentially beneficial bacteria that positively affect the host by enhancing the microbial balance and therefore restore the normal intestinal permeability and gut microecology. They also improve the intestine's immunological barrier function and reduce the generation of proinflammatory cytokines characteristic of allergic inflammation. In clinical trials probiotics appear to be useful for the treatment of various clinical conditions such as food allergy, AD and allergic rhinitis, and in primary prevention of atopy. We can hypothesize that it may be possible, in the future, to use probiotics in primary prevention of asthma.