Different Salmonella strains were tested for aerobactin production in a hydroxamate-bioassay with the aerobactin indicator strain E. coli LG 1522. The majority of hospital strains of Salmonella typhimurium produce hydroxamate siderophore. On the other hand S. typhimurium strains belonging to phage type n. c. 1/72/n. c., biochemical type b from human and animal sources, were unable to produce this siderophore. Serotypes other than S. typhimurium for example the multiresistent S. wien hospital strains, which were isolated in western europe and in the GDR, can excreate hydroxamate siderophore. Plasmids pIE 528 and pIE 5 234 isolated from Salmonella hospital strains produce hydroxamate siderophore in the enterobactin negative Salmonella typhimurium-strain enb-7. Thus, the hydroxamate bioassay may be a useful supplementary test for epidemiological strain characterization.