MucilAir, a 3D cell model of the human airway epithelium, could be a valuable in vitro tool for studying respiratory diseases and assessing inhaled toxicants in long-term or repeated dose toxicity testing. Therefore it is important to assess the stability of tissue morphology and function over time. This study assessed the stability of bronchial MucilAir tissues in three independent laboratories over 38 days of culture post-differentiation. The endpoints tested were transepithelial electrical resistance (TEER), cilia beat frequency (CBF) and mucin secretion, conducted simultaneously at all three test sites. TEER values were comparable and proved to be relatively stable over the culture period, despite one site having a slight increase in TEER after 14 days in culture. Similarly, CBF did not change markedly over time. However, the average CBF varied across the three sites, ranging from 9.73±0.16 to 12.26±0.15 Hz. Cilia active area measures were somewhat variable within day, but similar between two of the three test sites, with the third reporting generally lower percentages. A similar observation was made for mucin production with comparable values in two of the three test sites. However, the results obtained at the third test site were generally higher although reporting stable mucin production over the 38 days. Despite some minor differences between the test sites, the overall results demonstrated that the fully differentiated bronchial MucilAir tissue was stable over a 38 day culture at three independent laboratories. To support these initial findings, immunohistological analysis for specific cellular markers (p63, MUC5AC, FoxJ1, Ki67) is being employed to evaluate the frequency and distribution of cell types within the cultures before embarking on future studies using various test materials.