The involvement of the chemotaxis gene cluster 1 (cheYZABW and cheR in repellent responses of Pseudomonas aeruginosa to trichloroethylene (TCE) is described and three methyl-accepting chemotaxis proteins (MCPs) for TCE are identified. TCE chemotaxis assays of a number of deletion-insertion mutants of P aeruginosa PAO1 revealed that the chemotaxis gene cluster 1 and cheR are required for negative chemotaxis to TCE. Mutant strains which contained deletions in pctA, pctB and pctC showed decreased responses to TCE. The pctA, pctB and pctC genes have been reported to encode MCPs for amino acids [K. Taguchi et al., Microbiology, 143, 3223-3229 (2000)]. The pctA mutation more severely impaired chernotactic responses to TCE than did those of pctB and pctC, suggesting that PctA is the major MCP for TCE among the three MCPs. The pctA, pctB and pctC mutant strains showed decreased responses to chloroform and methylthiocyanate. This result demonstrates that P&A, PctB and PctC are also involved in repellent responses to chloroform and methylthiocyanate.