Removal of heavy metals from contaminated soil by chelation can be a valid remediation method, Important properties of the chelating agent used are: strength of the chelation bonding, reusability, and biostability during the remediation operation. This work tested the extraction, recovery, and biostability of diethylenetriaminepentaacetate (DTPA) as a remediation agent for soils contaminated with metals. Reported here are effects of parameters such as DTPA concentration, precipitant type and concentration, and pH relative to extraction and recovery efficiencies of the chelator, as well as workable recovery conditions. The assessment of biostability was determined at different DTPA concentrations, in aqueous and soil slurry systems, and in presence of lead using acclimated and unacclimated activated sludge cultures. The results showed that DTPA was capable of extracting lead from the tested contaminated soils and could be recovered by the use of cationic and anionic precipitants in alkaline pH conditions. It was biostable to some extent especially with unacclimated cultures. Thus, DTPA proved to be a strong and reusable chelating agent for some metals in soils, and it was relatively biostable, which makes it a valid remediation agent for soil metal extraction. (C) 2002 Elsevier Science B.V. All rights reserved.