The objectives of this proposal are to develop a scale for mutagenic/carcinogenic potential of environmental agents using the effects induced by exposure to ionizing radiation as the standard. The measurements will be based upon the responsiveness of rats; therefore, resulting in the development of a new and unique Tier Two Bioassay. The scale will be according to Radiation-equivalency (Radeq) which will represent the potential of environmental agents to induce cell-mediated immunity (CMI) and antibody-dependent cell cytotoxicity (ADCC) responses in inbred Fisher 344 rats as compared to the immune responses induced in the adult male rats which have had only their hypoxic ileum and jejunum exposed to X-irradiation. Threshold (T) levels will be obtained by a direct correlation of cytotoxicity to the exposure. Radeq will be determined by the construction of Lineweaver-Burk (1/cytotoxicity versus 1/exposure) plots and defined as the level of exposure to the environmental agent necessary to indue 1/2 the maximum cytotoxicity (CMI or ADCC) divided by the amount of X-ray exposure necessary to induce a similar 1/2 the total cytotoxicity. We have presented extensive data to support these concepts and have already calculated values for the colon carcinogen, 1, 2-dimethylhydrazine (DMH). The threshold detectable level was found for DMH to be T equals 1.7 umole (0.1 mg/kg animal weight, 0.1 ppm) and Radeq equals 186 nmole/R. Similar values will be tabulated for adult male and female rats, pregnant mother animals and their litters upon reaching adult size for exposure to DMH, 7, 12-dimethylbenz(a)anthracene and X-rays. The results will clearly indicate any variations due to age, sex, route of exposure and possible fetal tissue amplification (concentration). Further studies of this unique Tier Two Assay will be carried out to define, to a greater extent, specificity by testing substances shown to be positive or negative for mutagenecity/carcinogenicity by the Ames Salmonella microsome assay.