Objective: Lung epithelial type II cells were shown to respond with a complex intracellular Ca²⁺ signal mechanism to tensile stress, resulting in cellular responses such as surfactant exocytosis. The aim of our study was to investigate the mechanisms of Ca²⁺ mobilization in airway epithelial cells in response to non-damaging uni-axial cellular stretch. Methods: In our study we use Calu 3 cells as a well established lung adenocarcinoma cell line which forms functional epithelial cell layers. Cells were seeded on silastic membranes, mounted on a fluorescence microscope and exposed to uni-axial stretch. Cytoplasmic Ca²⁺ concentration ([Ca²⁺]_c) was measured ratiometrically using Fura-2. Results: An amplitude-dependent transient elevation of [Ca²⁺]_c was observed at stretch amplitudes of 30 % and more. Repetitive stretching of cells with an amplitude of 50 % resulted in a rundown of the stretch-induced [Ca²⁺]_c elevation. The elevation of [Ca²⁺]_c as well as the relative number cells responding with a Ca²⁺ signal was slightly reduced by depletion of extracellular Ca²⁺. An almost complete inhibition of the stretch-induced [Ca²⁺]_c elevation was achieved by emptying intracellular Ca²⁺ stores using thapsigargin and by the phospolipase C (PLC) inhibitor U71322. Conclusion: Our results strongly suggest that stretch-induced [Ca²⁺]_c elevation in Calu 3 cells is mediated predominantly by Ca²⁺ release from intracellular stores which is activated via PLC . This study was supported by the DFG, grant D1402