The major hypothesis of carcinogenesis is that malignancy is due to an alteration (mutation) of the genetic material in a somatic cell. Reactive electrophilic metabolites are generated from many chemicals by the action of endogenous mixed-function oxidases. These reactive metabolites may bind to cellular macromolecules, such as DNA, and can, therefore, initiate a mutagenic or carcinogenic event. Prokaryotes and non-mammalian eukaryotes are used in mutation assays, while cultured mammalian cells are generally used for mutagenic as well as clastogenic tests examining alterations and damage to the DNA and/or chromosomes of somatic cells. One of the first mammalian cell lines used in genotoxicity studies is V79, which was derived from Chinese hamster lung cells. According to the test plan on toxicity studies of mild gasification products, mammalian cell in vitro assays are to be performed on selected samples displaying mutagenic activity in the Ames assay. The results of the Ames testing of the mild gasification sample Shell Oil PSIS{number_sign}330331 were negative. However, fractionation of the sample and Ames testing of the subfractions were performed per DOE request. None of the subfractions was mutagenic in the Ames assay, as has been previously reported. Assays for the induction of gene mutation, sister chromatid exchange and micronucleus formation in V79 cells have also been carried out for the sample. This paper reports the results of the mammalian cell assay.