A new strain of Alcaligenes xylosoxydans able to aerobically cometabolize thiodiglycol, the primary hydrolysis product of sulfur mustard, was isolated and tested in a laboratory scale stirred tank reactor. The strain, named PGH10, cannot use TDG as sole carbon and energy source for growth, but resting cells previously grown on either rich broth or defined mineral media efficiently metabolize this compound through [(2-hydroxyethyl)thio]acetic acid and thiodiacetic acid as intermediates. Degradation of TDG by PGH10 is shown to take place at late exponential and stationary phase but is not triggered by carbon exhaustion. Cultures pregrown to saturation for 48 h in the absence of TDG can be stored and used for degradation of TDG, reducing significantly the time required to achieve the reduction of the compound concentration to undetectable levels. Degradation can take place in buffered media with no carbon source added, although best results were obtained in mineral media supplemented with citrate or fructose. Oxidation to [(2-hydroxyethyl)thio]acetic acid and thiodiacetic acid was proposed to be catalyzed by a butanol-dehydrogenase activity. Inhibition of TDG transformation in the presence of several alcohols is also shown.