The desire to alter the natural incidence of atopic illness has piqued physicians' imaginations for decades. Specifically, the phenotypic expression of IgE-mediated disorders, which appears regulated by multiple genetic factors and modulated by environmental experiences (allergen exposure, infection, and smoking), has been a target for preventive medicine since the 1920s when dietary intervention was espoused in infancy. To be successful, such intervention must overcome many patient factors that in concert markedly increase the risk for development of atopic disease (Table XII). During the past 60 years, much controversy has emerged from multiple clinical studies designed to evaluate the effect of dietary and other environmental exclusions on the subsequent manifestation of atopy. One may conservatively conclude, from critical evaluation of these conflicting studies, that sole breast feeding for about 6 months combined with delayed introduction of solid foods for at least 6 months may reduce atopic dermatitis and food allergy in early infancy. A randomized, prospective study of allergy prophylaxis during infancy is mandatory to determine definitely the benefits and feasibility of such a regimen and its long-term effects on the development of atopy. From our recent findings, which demonstrate the development of atopy in infants entered in a strict prophylactic protocol, it becomes apparent that monumental obstacles confront preventive efforts to overcome the strength of the allergic constitution. In the very near future, results from our prospective study of prenatally randomized allergy prophylaxis should be available for critical scrutiny of the effectiveness and feasibility of allergy prevention during infancy.