The influence of metal ions on the metabolism of ethylenediaminetetraacetate (EDTA) by whole cells and cell-free extracts of strain BNC1 was investigated. Metal-EDTA chelates with thermodynamic stability constants below 10(12) were readily mineralized by whole cells with maximum specific turnover rates of 15 (MnEDTA) to 20 (Ca-, Mg-, and BaEDTA) mu mol g protein(-1) min(-1). With the exception of ZnEDTA, chelates with stability constants greater than 10(12) were not oxidized at a significant rate. However, it was shown for Fe(III)EDTA that even strong complexes can be degraded after pretreatment by addition of calcium and magnesium salts in the pH range 9-11. The range of EDTA chelates converted by cell-free extracts of strain BNC1 did not depend on their thermodynamic stabilities. The EDTA chelates of Ba2+, Co2+, Mg2+, Mn2+ and Zn2+ were oxidized whereas Ca-, Cd-, Cu-, Fe-, Pb-, and SnEDTA were not. The first catabolic enzyme appears to be an EDTA monooxygenase since it requires O-2, NADH, and FMN for its activity and yields glyoxylate and ethylenediaminetriacetate as products. The latter is further degraded via N,N＇-ethylenediaminediacetate. The maximum specific turnover rate with MgEDTA, the favoured EDTA species, was 50-130 mu mol g protein(-1) min(-1), and the K-m value was 120 mu mol/l (K-s for whole cells = 8 mu mol/l). Whole cells as well as cell-free extracts of strain BNC1 also converted several structural analogues of EDTA.