In environmental health, inhalation is the most prominent route of ethylene oxide (EO) exposure. In the current study, human embryonic pulmonary epithelial cells (L132 cell line) were exposed to EO following a prior adaptation to atmospheric conditions. A comparative study between two EO exposure conditions (0.07 and 0.18 g/m3 gas injections) was carried out after a 1-h incubation. Whereas control cells were exposed to a pure air stream. The EO cytotoxicity was established by electron microscopy and LDH and ATP determinations after 1, 3, 6 and 24 h following the exposure. The ultrastructural examination revealed a remarkable vacuolisation of the exposed cells leading to cell death. In spite of this modification, the number of mitochondria and the content of endoplasmic reticulum increased in the L132 cells. For both exposure concentrations LDH was released into the extracellular milieu. In the presence of the high EO concentration, LDH activity increased with respect to the post-exposure time involving alteration of the membrane and permeability. For low EO exposure, ATP synthesis was significantly increased after 1 h of post-exposure (P < 0.01) and decreased to normal levels after 6 h. For the high EO concentration, however, ATP continually increased with respect to the post-exposure time. This indicates cellular stimulation and suggests the activation of a defense mechanism. This study shows a direct EO cytotoxicity on L132 cells cultured in atmospheric conditions.