The pathogenesis of Pseudomonas aeruginosa is at least partially attributable to its ability to synthesize and secrete the siderophore pyoverdin and the two zinc metalloproteases elastase and LasA, and its ability to form biofilms in which bacterial cells are embedded in an alginate matrix. In the present study, a lysophospholipid, 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphate [also called monopalmitoylphosphatidic acid (MPPA)], which accumulates in inflammatory exudates, was shown to inhibit the extracellular accumulation of P. aeruginosa PAO1 alginate, elastase, LasA protease and the siderophore pyoverdin. MPPA also inhibited biofilm formation. The inhibitory effects of MPPA occur independently of rpoS expression and without affecting the accumulation of the autoinducers N-(3-oxododecanoyl) homoserine lactone and N-butyryl-L-homoserine lactone, and may be due, at least in part, to the ability of MPPA to bind divalent cations.