Ventilator induced lung injury (VILI) is a live threatening complication in patients submitted to artificial ventilation. We investigated mechanisms of stretch induced cell damage in alveolar epithelial cells. Isolated alveolar type II (ATII) cells from rat were cultivated on silastic membranes and exposed to uni-axial stretch at a velocity of 10 % per second. ATII cell damage was detected by ethidium homodimere (EHD) uptake under microscopic surveillance. Cellular damage was observed at stretch amplitudes above 15 %, and more than 90 % of cells were damaged after applying stretch amplitudes of 40 %. Cells, which resisted a single stretch of certain amplitude, remained undamaged even after applying 9 repetitive stretches of the same amplitude with a frequency of 0.125 Hz. Cytoskeleton components were labelled and detected by fluorescence microscopy in fixated ATII cells after cells were submitted to a single stretch with an amplitude of 40 %. No changes of the tubulin and cytokeratine network in stretched cells compared to un-stretched control cells were detected in these experiments, whereas actin fibres were significantly disrupted in stretched ATII cells. Actin depolymerisation by pre-incubation of cells with 10 mM cytochalasin D did not sensitize ATII cells to mechanical stretch. These results implicate stretch amplitude rather than stretch repetition as a crucial cell damaging determinant. Furthermore, stretch induced cell damage is accompanied by disruption of actin fibres, whereas actin fibres do not seem to contribute to cellular stretch resistance. Our results give further support to ventilatory protocols using low tidal volumes in order to prevent VILI. Supported by DFG, grant D1402 and the Landesstiftung Baden Württemberg