The rationale in approaching each stress agent will be to first consider the relative resistance of lepidopteran cells compared to cells of mammalian or other origin. A number of studies on a variety of insect species indicate that insects have considerably more inherent resistance to the lethal effects of ionizing radiation than most other organisms. Our current understanding of the molecular mechanism of lepidopteran cell resistance to the various physical and chemical agents discussed is clouded somewhat by the apparent inconsistencies in the data obtained. The degree of radioresistance corresponds to insect order, with lepidoptera being by far the most resistant. It has been demonstrated that cells cultured from insects are considerably less sensitive to ionizing radiation-induced killing than cultured mammalian cells. In the mid 1970s, however, it was discovered that the TN-368 lepidopteran insect cell line exhibited a pronounced intrinsic resistance to the lethal effects of ionizing radiation.