The fate of the volatile organic compound, 1,4-dichlorobenzene (DCB) was examined in a bench-scale activated sludge system. A shift in removal mechanism, from stripping to biodegradation, was observed at different stages of acclimation. The response of an unacclimated sludge to DCB perturbations showed a preferential loss of DCB by stripping. Radiolabeled DCB tracer studies with an acclimated sludge demonstrated 10 to 20% mineralization of DCB, 25 to 30% loss by stripping, and the remaining DCB transformed to intermediate metabolites that were found in the mixed liquor and effluent. Biodegradation rates determined for DCB fell into two distinct ranges depending on the degree of sludge acclimation.