In Pseudomonas aeruginosa, quorum sensing (QS) autoinducer known as acyl homoserine lactone (AHL) acts as a key regulator in the expression of pathogenic characters. In this work, the efficiency of phenylacetic acid (PAA) in reducing the production of AHL-dependent factors in P. aeruginosa PAO1 was studied. PAA at a concentration of 200 mu g ml(-1) displayed significant reduction in QS-dependent pyocyanin, exopolysaccharide, and protease and elastase production in PAO1. In swimming inhibition assay, PAA-treated PAO1 cells exhibited poor motility in swimming agar plate. In in vivo analysis, PAO1-preinfected Caenorhabditis elegans showed enhanced survival when treated with PAA. PAA at the QS inhibitory concentration showed no growth inhibitory activity on PAO1. Results of the present study revealed the potential of PAA as antipathogenic compound to prevent QS-dependent pathogenicity of P. aeruginosa.