The report, based on a survey of published literature, establishes a set of sensitivity estimates for the Level 1 environmental assessment (EA) bioassays recommended by EPA's IERL-RTP. The estimates permit comparison of bioassay sensitivity for detecting toxicity or mutagenicity of pure chemicals and also estimation of the concentrations of toxic materials that could be in a mixture that registers negative in a particular test. Three tests--Ames Salmonella/microsome mutagenesis assay, in vitro rodent cell (CHO) clonal toxicity assay, and in vivo rodent toxicity assay--have substantial published data bases using study designs similar to those used in Level 1 EA tests. The report summarizes the sensitivity limits for detecting toxicity or mutagenicity for a variety of pure compounds with these three tests. Methods developed to assess these data will be applicable to other Level 1 tests such as the rabbit alveolar macrophage (RAM) assay and the aquatic and other ecological assays. However, these evaluations await the development of a sufficient data base with a wide variety of pure compounds. Two of the reviewed bioassays (Ames and CHO) were found to approach the sensitivity required of the Level 1 chemical analytical procedures.