Research Signficance: Airways represent an important portal of entry for nanomaterials (NM) and in vitro tests to evaluate the respiratory toxicity of NM are badly needed. Airway epithelium is the first barrier encountered by inhaled NM and the interaction between them and the epithelial cells markedly influences the exposure outcome. Metal nanoparticles (MNP) are increasingly produced and used, but their effects on airway epithelium are largely unknown. To elucidate this issue, human airway cell monolayers were incubated with two nanometric preparations of CeO2 and three preparations of TiO2 (anatase:brookite; anatase:rutile; rutile); CuO NP were used as positive controls. Methods: The experiments were performed with confluent Calu-3 cells, grown on permeable filters, where they form a high-resistance monolayer, providing an in vitro model of airway barrier. MNP were characterized under the conditions adopted for the biological tests. The apical side of the monolayer was exposed to MNP for 7 days. Epithelial barrier permeability was monitored measuring the trans-epithelial electrical resistance (TEER) and cell viability was assessed through the resazurin method. Result: In the whole range of nominal doses tested (10-100 μg/cm2 of monolayer), CuO NP produced a marked decrease of TEER, indicating that the permeability was increased and the epithelial barrier impaired. TEER decreased by 30% at 10 μg/cm2, in the absence of effects on cell viability, and was abolished at doses 80 μg/cm2, where the viability was completely suppressed. At the same doses, neither CeO2 nor TiO2 NP had significant effects on cell viability or TEER. Conclusion: These results indicate that (1) CuO NP markedly increase airway barrier permeability even at relatively low doses; (2) different forms of TiO2 and CeO2 NP have a low toxicity for airway epithelial cells; and (3) TEER measurements can provide a simple method to assess the toxicity of NM on the airway barrier.