Aerobic biodegradation of the chelating agent EDTA by a mixed bacterial culture was investigated. Bacterial growth and degradation of the substrate required the presence of sufficient metal ions in the culture fluid. Uncomplexed EDTA interacted negatively with the cell walls of the bacteria and completely inhibited bacterial growth, whereas Mg(II)/Ca(II)-EDTA was degraded up to an initial concentration of 4.7 g/l. Therefore, concentrations of metal ions must be stoichiometric to that of EDTA or higher. Specific degradation rates ranged between 120 mg EDTA g(-1) (cell dry weight) h(-1) and 285 mg EDTA g(-1) h(-1). In contrast, complexes with high thermodynamic stability constants such as Fe(III)-EDTA remained as inert compounds in the solution. Specific growth rates of the mixed culture were found to vary between 0.03 h(-1) and 0.07 h(-1), which could be explained by population dynamics within the synergistic mixed community. Growth was significantly accelerated by the addition of vitamins.