~ ~~ ~~ ~~ ~~ ~ ~ ~~ ~ ~ ~ In iron-deficient conditions of growth Pseudomonas cepacia ATCC 2541 6 excreted both pyochelin and a low-molecular-mass compound which strongly chelated iron(III), and facilitated iron translocation as demonstrated by growth and uptake experiments. The name cepabactin is proposed for this new siderophore. Comparisons of UV-visible spectra and chromatographic behaviour, together with H-NMR spectra, led to the conclusion that cepabactin is 1 -hydroxy-5-methoxy-6-methyl-2( 1 H)-pyridinone, a compound which can be considered as a cyclic hydroxamate, but also as a heterocyclic analogue of catechol. This pyridinone has already been described by other workers as an antibiotic produced by Pseudomonas alcaligenes, and by a soil isolate closely related to Pseudomonas cepacia. Thus, cepabactin appears to act as a siderophore for more than one species of non-fluorescent pseudomonad.