A database of results has been created using chemicals tested by the NTP for mutagenesis in short-term assays, and for carcinogenesis. This database allows the evaluation of each short-term assay with respect to its ability to predict carcinogenesis or other short-term assay results. It also permits studies of the individual assays with respect to inter and intra-laboratory reproducibility, and the effects of protocol changes on test responses. A study is underway to examine the predictivity of the four short-term tests as a function of the potency of the short-term test and carcinogenicity test responses. The chemicals to be evaluated include the 73- and 41-chemical datasets studied earlier in a project to correlate short-term test results with carcinogenicity results, based on qualitative results. As a result of that project, the same chemicals, in the same test systems, will be examined to determine how well the potencies of the responses correlate. A part of this study involves the development of measures of potency for the different tests. Such measures have been proposed by others for the Salmonella and carcinogenesis assays, but there are no commonly-accepted measures of potency for the other short-term tests, such as in vitro chromosome aberrations, in vitro SCE, or the mouse lymphoma assay. These measures of potency are being developed and evaluated, and will be used for the correlational studies. Different potency measures for the Salmonella test have been compared; the procedures developed by Margolin et al. and Bernstein et al. which model an initial slope give comparable values. Procedures that provide measures other than slopes will be evaluated and one of these procedures will be used in conjunction with the slope procedures.