The materials contained in this Salmonella Mutagenicity Assay Kit include virtually all of the supplies necessary for the conduct of the “Ames Assay” as described by Maron & Ames (Maron, D. M. and B. N. Ames, Revised methods for the Salmonella mutagenicity test, Mutation Research, 113: 173-215, 1983) and Mortelmans & Zeiger (Mortelmans, K. and E. Zeiger, The Ames Salmonella/microsome mutagenicity assay, Mutation Research, 455: 29-60, 2000). We strongly recommend that you carefully read one of these papers and OECD guideline 471 before you attempt to perform the assay. The MOLTOX® kit contains four tester strains; TA1535, TA1537, TA98, and TA100. Each strain was constructed with a different lesion in the histidine operon. This mutation renders them incapable of synthesizing histidine, i.e. they are histidine auxotrophs requiring exogenous histidine. In addition, TA1535, TA1537, TA98, and TA100 have altered cell walls (rfa) that increase the cell’s permeability to certain high molecular weight materials. These strains also share a lesion in a DNA repair-coding gene (uvrB) which results in an increase in sensitivity to a variety of mutagens [since this lesion extends through the gene for biotin synthesis (bio), biotin is also required for growth]. Tester strains TA98 and TA100 carry a plasmid (pKM101) which acts to increase the activity of an error-prone DNA repair system and to confer resistance to the antibiotic ampicillin; TA1535 and TA1537 contain no plasmids. The MOLTOX® Salmonella Mutagenicity Test Kit includes sufficient components for testing 1 unknown sample, in triplicate analysis of 5 concentrations, positive and negative controls, with and without S9.