Although a number of test protocols have been developed to predict respiratory allergenic potential, none of these are widely applied or fully accepted. However, given the serious health problems caused by respiratory allergy and the ever-increasing stream of new chemicals into workplaces, early identification of chemical respiratory allergens is important. Inhalation exposure as well as skin application have been used in predictive tests to induce respiratory tract sensitisation. While there are good indications in laboratory animals and humans that skin exposure can act as a route for respiratory tract sensitisation and vice versa, less is known about the effect of the route on the type of allergy evoked and on dose-response relationships. Although, the responses were in general more vigorous after dermal sensitisation than after inhalation sensitisation, the nature of the immune responses seemed to be qualitatively comparable. As to the intensity of exposure, dose or concentration-response relationships have been observed both during respiratory sensitisation and challenge, suggesting that assessment of safe exposure levels is feasible. Finally, a correct distinction between respiratory allergens and non-sensitising airway irritants is needed for effective risk assessment and management. © 2003 Elsevier Science Ireland Ltd. All rights reserved.