An experimental in vitro model was established to study the effects of environmentally relevant gaseous compounds on lung cells. The technical unit consists of a gas reaction chamber (2400 l) with a sun-simulator to produce and photochemically transform gaseous mixtures and compounds at the upper limit of environmentally relevant concentrations. Rat lung cells were exposed on transwells in a perspex chamber inside an incubator, into which the gaseous mixtures were conducted. Analysis of the gas phase was performed inside the reaction chamber and at the outlet of the exposure box to assess the effective exposure concentrations. The growth of the cells on PET-membranes allowed direct cell exposure with a minimal barrier for contact between gas and cells. To assess the cytotoxicity, the following biochemical markers for the cellular status after exposure were determined: amount of dsDNA, WST, BrdU-incorporation after exposure, LDH release into the culture medium, activity of glutathione S-transferases and esterases. Using this system, dose-dependent cytotoxicity was found for NO2 in the concentration range from 80 to 360 ppb and strong cytotoxic effects for ozone in the concentration range from 225 to 500 ppb. Exposure to purified air did not show significant effects. In addition, some irradiated gas mixtures (photo smog) showed cytotoxicity whereas non-irradiated mixtures did not.