The prevalence of allergic diseases, such as allergic asthma, allergic rhinitis and atopic dermatitis, has increased during the last decade. It is generally accepted that the increased prevalence of allergic diseases is due to a disturbed T-helper lymphocyte (Th) Th1-Th2 balance, leading to more expression of Th2 features. Decreased postnatal microbiological stimulation (i.e. improvements in public health, reduction in family size, increased usage of antibiotics) results in an increased possibility of ongoing postnatal Th2 reactions. Furthermore, increased postnatal allergen exposure, especially to house dust mite, is known to facilitate the existance of Th2 features. Therefore, identification of early markers of allergy such as increased total IgE in cord blood offers the possibility to initiate adequate primary prevention in subjects at risk. Primary prevention measures constitute merely of avoidance of early allergen contacts (foods and inhalants) and avoidance of pollution exposure (i.e. passive smoking). At the moment, insufficient data are available concerning the preventive effect of medication on the development of allergic diseases. However, studies on the early use of cetirizine suggest that the occurrence of asthma can be prevented or delayed in young children suffering from atopic eczema. Conclusion: because identification of the atopic newborn is now possible, adequate early prevention can be instigated.