The influence of surfactants on a perchloroethene dechlorinating mixed culture was investigated in laboratory experiments. Seven surfactants, representing each of the surfactant classes, were screened for their effects on the rate and extent of perchloroethene dechlorination. Based on screening results, a nonionic surfactant, Tween 80, and an anionic surfactant, Steol CS-330, were selected for use in further studies. Dechlorination of perchloroethene to dichloroethene, vinyl chloride, and ethene occurred in all Tween 80 amended microcosms with a depressed rate of ethene production as the only adverse effect. Steol CS-330, however, inhibited dechlorination beyond dichloroethene at all surfactant concentrations exceeding 25 mg/L. Attempts to acclimate a culture to the surfactant were unsuccessful. Inhibition of vinyl chloride and ethene production was reversible upon dilution of the surfactant to 10 mg/L or below indicating that surfactant interactions with the enzyme system responsible for reductive dechlorination of dichloroethene was the most likely cause of inhibition.