The umuC assay is based on the SOS response in S. typhimurium TA1535 pSK1002. The SOS response is induced as a consequence to DNA damage or disruption of DNA replication. The reporter fusion gene umuC-lacZ on the plasmid pSK1002 is expressed as a consequence of mutational events induced by chemicals or UV radiation. This test is rapid and responds to chemicals with various mutational mechanisms, including cross linking events. The Xenometrix umuC Easy assays are based on the ISO 13829 international standard protocol using the same media and reagents. We have, however, modified the procedure for easier handling and provide an Excel calculation template for all necessary calculations. Xenometrix offers 2 versions of the kit: umuC Easy AQ for testing of aqueous samples, and umuC Easy CS for testing of concentrated samples like chemicals or extracts. Both umuC Easy kits have sufficient bacteria and reagents to perform 2 x 96 determinations. This allows to test 2 x 3 samples according to ISO 13829 in 4 dilutions, triplicate values, positive and negative controls, with and without S9 metabolic activation.