Novel citrate-hydroxamate siderophores, named nannochelins A, B and C, were isolated from the culture broth of the myxobacterium Nannocystis exedens strain Na e485. The new substances showed weak growth-inhibitory activity against some bacteria and fungi. During our screening program for new biologically active compounds from myxobacteria, we found that many Nannocystis strains produced substances that inhibited the growth of some Gram-positive bacteria and showed positive reactions with FeCl3 on TLC. The activity from Nannocystis exedens strain Na e485 was further investigated and could be characterized as a new group of siderophores, which were named nannochelins. Structural elucidation revealed that the so far isolated variants, nannochelins A, B and C, were derivatives of citric acid, with the terminal carboxyl groups of the citric acid linked in an amide-like fashion with two molecules of N-ε-cinnamoyl hydroxylysine-methyl ester (Fig. 1). The nannochelins are thus structurally related to other members of the citrate-hydroxamate family, such as schizokinen, arthrobactin and aerobactin. In this paper we describe the production, isolation and some of the physico-chemical properties of nannochelins A, B and C, while the structure elucidation will be published elsewhere.