Erwinia amylovora, the etiological agent of fire blight, produces a family of proferrioxamine siderophores, which may be essential for the pathogen to establish itself in its hosts. If so, then control of fire blight may perhaps be possible via interference with proferrioxamine biosynthesis. Proof of this hypothesis requires prior knowledge of the corresponding biosynthetic pathways in E. amylovora. As a first step towards understanding proferrioxamine biosynthesis, it was of interest to investigate the ability of the fire blight bacterium to utilize various potential biosynthetic pathways for diamines. Feeding of lysine, ornithine and diaminobutyric acid gave rise to highly elevated levels of cadaverine, putrescine and diaminopropane, respectively, indicating that the corresponding decarboxylase activities are all present in E. amylovora. The conclusion for lysine decarboxylase was confirmed with (15N2)lysine, which was converted to (15N2)cadaverine. Arginine did not increase putrescine levels substantially, but (13C6)arginine nevertheless gave rise to (13C4)putrescine while suppressing excretion of non-labeled putrescine. A serendipitous result of this study was the finding that the growth of E. amylovora can be inhibited with 5-hydroxylysine and 1,4-diamino-2-butanone. The mechanism of inhibition appears complex and is not yet understood. For 5-hydroxylysine, preliminary investigations point to a competitive inhibition of lysine decarboxylase. However, the growth inhibition cannot be reversed by providing cadaverine, the decarboxylation product of lysine.