Methods were developed for exposing cells in vitro to gases or vapors of volatilized organic liquids. Compounds were selected for their industrial importance, environmental impact, and suspected role in the etilogy of some human cancers. Exposure chambers were designed for easy insertion of dishes of cultured cells and were equipped with inlet and outlet ports for introduction and purging of test gases. A gas delivery system utilizing a mass flow meter was used for the quantitative distribution of test gases into exposure chambers. For volatile compounds, appropriate volumes of cold (4 deg) liquids in glass Petri dishes were quickly placed into chambers, the system sealed, and the compounds rapidly volatilized at 37. For exposure, the cells and chambers were placed in an incubator and rocked at a constant rate so that a portion of the cells was always in direct contact with the test gases or vapors.