Some general principles of mutagenicity screening and a possible framework for testing procedures.

It is likely that the assessment of chemicals for mutagenicity will soon become a widespread practice, and a large number of different screening procedures have been proposed. The subjection of every new chemical to be released into the environment to every available test is clearly an impossible task, and it is necessary for an understanding of priorities in terms of risk and benefit to be built into any approach. The present paper represents an attempt to frame a protocol for the assessment of new compounds that is concerned not with the details of individual tests but rather with the questions these tests should be designed to answer and to the evaluation of the answers obtained. It is obviously inherent in such an approach that a similar assessment must be made of chemicals already in the environment, but that is not the purpose of the present article. Genetic hazards (with the exception of nondisjunction and some other chromosomal abnormalities) are very different from toxic hazards, in that there is little or no likelihood of any feedback from human epidemiological data. Toxicologists have stressed (1) that, despite all the animal testing of the past two decades and before, most of what we know about toxic hazards