AbstractIn vivo and in vitro methodologies that have employed the yeastSchizosaccharomyces pombeas genetic indicator have been utilized to investigate the mutagenicity of two trichloroethylene (TCE) samples of pure and technical grade. Mutagenicity assays were also performed on two stabilizers contained in the technical grade sample: epichlorohydrin and 1,2‐epoxybutane.In the in vitro studies a metabolic conversion system was supplied by liver homogenate (S‐9) from mice and rats untreated and pretreated with phenobarbital and/or β‐naphthoflavone. Up to highly toxic doses of TCE were applied to growing and stationary‐phase yeast cells.In the in vivo studies two different host‐mediated assays, intrasanguineous and intraperitoneal methodologies, were performed on different mice breeds treated by oral administration.Epichlorohydrin and epoxybutane were tested singly or combined in a mixture of the same ratio as in the technical grade TCE sample.Both TCE samples gave negative results for in vivo and in vitro assays, whereas the two contaminants were found mutagenic only in vitro. The high toxicity of the technical TCE sample did not allow us to reach concentrations containing effective levels of its two