Biosynthesis of ethylene by the Kudzu strain of Pseudomonas syringae pv. phaseolicola causing halo blight in Kidney bean plants was studied. Ethylene was effectively produced from the bacteria incubated with the Krebs cycle intermediates and related organic acids. Ethylene was continuously produced throughout a 6 h incubation period from Asp, OAA and KG supplied in the medium as substrates, but the rate of glutamic acid-based ethylene production decreased sharply following incubation for about 3 h Ethylene production induced by Succ, Fum, Mal, OAA and Pyr was further enhanced by arginine whereas citric acid- and KG-induced ethylene production was not affected. The rate of ethylene production with the Krebs cycle organic acids was in order of: Pyr>OAA>Mal>Fum>Succ>KG>Citr. Monofluoroacetate and, inhibitor of the Krebs cycle enzymes, and aminooxyacetate and L-canaline, both inhibitors of a PLP-linked enzyme, inhibited ethylene production induced by Glu and Asp, but not that induced by OAA and Pyruvate. The results obtained in this work suggest that either OAA or Pyruvate is a more direct precursor of bacterial ethylene production than any other organic acids tested.