Epidemiological data show that allergic children have a different intestinal flora from healthy children with higher levels of Clostridia and lower levels of Bifidobacteria. Nonetheless, Bifidobacteria and Lactobacilli are found more commonly in the composition of the intestinal flora of non-allergic children. Probiotics are ingested live microbes that can modify intestinal microbial populations in a way that benefits the host and they are represented mainly by Lactobacilli. Enhanced presence of probiotic bacteria in the intestinal microbiota is found to correlate with protection against atopy. There is also very promising evidence to recommend the addition of probiotics to foods for the prevention and treatment of allergic diseases. Clinical improvement, especially in allergic rhinitis and immunoglobulin (Ig)E-sensitized (atopic) eczema, has been reported in most of the published studies. However, clinical benefit of probiotic therapy depends upon numerous factors, such as type of bacterium, dosing regimen, delivery method and other underlying host factors, e.g. the age and diet of the host. Selection of the most beneficial probiotic strain, the dose and the timing of supplementation still need to be determined. This review helps understanding of the role of probiotics in various allergic diseases, explaining laboratory and clinical data in light of recent literature.