An approach for determining the biodegradability of new detergent builders under activated sludge conditions was investigated using carboxymethyltartronate (CMT) as a representative material. Preliminary biodegradation studies in river water and activated sludge indicated a 4–8 week period before acclimation to and biodegradation of CMT. More detailed studies in continuous flow activated sludge units established that acclimation to CMT degradation was not readily lost upon CMT starvation, could be maintained at low temperatures and under conditions of variable organic loading, and was unaffected by the presence of a variety of metal ions. The laboratory evaluation of CMT, which stressed the use of natural sewage/activated sludge systems in place of tests employing commercially available laboratory media, would predict CMT to be satisfactorily removed in full-scale activated sludge waste treatment plants.