Evidence has been found for the presence of an oxazoline ring in a siderophore from Paracoccus denitrificans. This requires revision of the previously assigned structure for this compound. Siderophores, defined as high affinity ferric ion transport agents from microbial sources may, in general, be grouped as hydroxamic acids or catechols. Ferrichrome and enterobactin are prototypes of the two classes, respectively. In 1975 Tait described a new member of the catechol series, designated compound III (I_, R=H; N1,N8-bis(2,3-dihydroxybenzoyl)-N4-(N-salicylthreonyl)-spermidine) from iron starved cultures of Micrococcus (now Paracoccus) denitrificans. Recently we isolated and characterized a closely related substance, named agrobactin (I& R=OH; N-(3-(2,3-dihydroxybenzamido)propyl)-N-(4-(2,3-dihydroxybenzamido)butyl)-2-(2,3 dihydroxyphenyl)-trans-5-methyloxazoline-4-carboxamide) from the phytopathogenic bacterium Agrobacterium tumefaciens. The presence of an oxazoline moiety in agrobactin and also in the previously discovered mycobactins, siderophores of mycobacterial species, prompted us to search for such a ring in the substance isolated by Tait. In this communication we confirm the presence of an oxazoline ring in compound III. The revised structure is therefore N-(3-(2,3-dihydroxybenzamido)propyl)-N-(4-(2,3-dihydroxybenzamido)butyl)-2-(2-hydroxyphenyl)-5-methyloxazoline-4-carboxamide (IJ, R=H) which we propose to call parabactin. By analogy with agrobactin, the structure given by Tait for compound III, i.e. the open form (I_, R=H), is designated parabactin A.