Lipoxygenase/hydroperoxide lyase generated compounds are thought to be important in plant defense. The effects of volatile compounds from this pathway on the proliferation of Escherichia coli TB1, Pseudomonas syringae pv. tabaci, and Pseudomonas syringae pv. angulata were evaluated. The vapor-phase concentrations of compounds in the bioassay system were estimated by gas chromatography. At the highest concentrations tested, the C 6 aldehyde (E)-2-hexenal completely inhibited proliferation of both P. syringae pathovars (570 μg/L of air) and E. coli (930 μg/L of air)