Polydimethylsiloxane (PDMS) fluid was evaluated for mutagenic potential in the Salmonella typhimurium and Escherichia coli Reverse Mutation assays as described in EEC Directive No.L251. Mutagenicity was evaluated by measuring the ability of PDMS fluid to produce reverse mutations in several strains of Salmonella typhimurium (TA1535, TA1537, TA98, TA100) and Escherichia coli (WP2) in the presence and absence of Aroclor-induced rat liver microsomal enzymes. Concentrations of 0 (solvent control), 312.5, 625, 1250, 2500, and 5000 ug/plate, along with positive controls, were plated with each tester strain in the presence or absence of microsomal enzymes. Sodium azide, 9-amino acridine, 2- nitrofluorene, n-methyl-n-nitrosoguanidine, and 2-anthramine served as positive controls. Initially, contamination was observed in the TA98 and WP2 plates, and these tests were rerun. No mutagenic responses were observed in any strain tested in the absence or presence of microsomal enzymes. Under the conditions of this study, PDMS fluid was not mutagenic.