This guide is limited to procedures used solely for the testing of substances to determine their mutagenicity and does not apply to other methods and uses such as exploring mechanisms of mutation.

Recent evidence suggests that this assay measures a dual genetic end point; therefore, some discussion of the relationships between mammalian cell mutagenicity testing results and the results observed both in pure gene mutational assays and in cytogenetic assays is necessary. However, it is not the intent of this guide to discuss other relationships between this mammalian cell mutagenicity testing results and the results observed in other tests for mutagenicity and carcinogenicity.

1.1 The purpose and scope of this guide is to present background material and to establish criteria by which protocols and procedures for conducting the L5178Y/TK^+/-3.7.2C mouse lymphoma mutagenicity assay (commonly referred to as the mouse lymphoma assay, (MLA)) can be properly understood and evaluated. This guide is also intended to aid researchers and others to gain a better understanding of the critical elements involved with mammalian cell mutagenicity testing. More specifically, this guide is intended to provide for researchers the accomplishment of the following goals:

1.1.1 Provide an understanding of the critical procedures (steps) in the performance of this mammalian cell mutagenicity test.

1.1.2 Provide generalized criteria by which researchers can evaluate if they are properly performing, utilizing, and interpreting this assay.

1.1.3 Provide criteria by which individuals responsible for evaluating MLA data can determine if the experiments have been properly performed and interpreted.

1.1.4 Provide a basis from which new procedures and developments in testing procedures can be evaluated.

1.1.5 Provide an understanding of the types of genetic damage (that is, gene and chromosome mutation) that may be detected in this mammalian cell mutagenicity test.