Epidemiological studies indicate a world-wide and significant increase in atopic diseases over the past decades, which has adopted alarming dimensions within the industrialized world. However, allergic asthma and pollinosis, in particular, are on the increase in Third world countries, in parallel to the industrialization and westernization of their life-style. Since both antigen exposure and the presence of additional realization factors are required for the manifestation of atopic diseases, this increase in prevalence is not surprising. In addition to increased indoor and outdoor pollution, changes in the way of living--causing increased allergen exposure--certainly play an important role as cofactor in the increased incidence of allergies. Accurate diagnostic procedures permit a better understanding of the realization factors for allergic diseases in epidemiological studies and identification of the causative agent in the individual so that effective therapeutic and prophylactic steps can be taken. Despite improved in vivo and in vitro test methods, the case history is still of paramount importance in reaching a diagnosis; the potential hazards of skin and provocation testing, as well as the high costs and limitations of in vitro methods prohibit "blind allergy screening".