PURPOSE OF THE REVIEW: Recent studies on the pathogenesis of allergy in both man and experimental animals continue to show the importance of commensal bacteria in the gastrointestinal tract in stimulating and directing the immune system. The interest in modulating commensal bacterial flora with prebiotics and probiotics to prevent and treat food allergy has multiplied in recent years. RECENT FINDINGS: Studies on prevention suggest that probiotic supplementation reduces IgE-associated eczema. It seems that prenatal administration is of importance. Colonization seems to be readily achieved, so there is proof of concept. However, after cessation of the administration, a rapid decline in colonization is evident. IgE sensitization in atopic eczema is a risk factor for allergic airways disease, and the reduced IgE-associated atopic eczema demonstrated may be an indication of less respiratory allergic disease later. Administration of probiotics to children with allergy or at risk of allergy seems to stimulate a low-grade inflammation by activating the innate immune system and further production of IL-10. SUMMARY: Modulation of commensal bacteria of the gut with probiotics has been shown to modulate the immune system and to have an effect on both the prevention and treatment of food allergy. The effects have been highly variable depending on the mode of treatment and the optimal treatment remains unsettled at present.