The long-term objective of this ongoing project remains the development of appropriate statistical techniques for the analysis of data arising from short-term assays under study NTP. Statistical procedures for the design and analysis of short-term tests proposed or currently employed by other researchers in mutagenicity are assessed and new and improved procedures are developed. Results are applicable to large mutagenicity studies, such as the European Collaborative Study and the International Program for the Evaluation of Short-Term Tests for Carcinogenicity. The major focus to date has been on microbial test systems, although additional research has dealt with Drosophila tests. Work on in vivo and in vitro cytogenic assays continues.