Traditionally, allergic rhinitis and bronchial asthma are described as distinct and separate entities. However, progress made in recent years has brought some great changes in the understanding of pathophysiology of allergic disorders. It has become clear that both of these disorders are characterised by similar triggers, inflammatory cells and mediators involved in their pathogenesis and treatment modalities. The link between these two airway disorders has led to the development of the so called "integrated airway hypothesis". According to this hypothesis allergic rhinitis and bronchial asthma are regarded as different facets of a generalised inflammatory process involving, although in a different degree, both the upper and lower airways. This review critically discusses the present state of knowledge on the links between the upper and lower airways in asthma and rhinitis on the basis of the recent literature and our own experience. We try to assess the importance of these links for the future diagnosis and treatment of allergic disorders of the respiratory tract.