Acetone and ethyl acetate were readily degraded in batch reactors containing anaerobic solids from an industrial reactor at concentrations to 1000 mg/L; isoamyl acetate was degraded at concentrations below 200 mg/L. Xylene was noninhibitory in batch cultures at concentrations of 50 mg/L or less. Batch reactors receiving 45 mg/L methylene chloride (MC) experienced a 60% reduction in gas production, and an increase in volatile fatty acids. Semicontinuously-fed reactors dosed with 20 mg/L MC at the start suffered some loss of anaerobic efficiency, but acclimated well with increased gas production after 20 d. A continuously fed sludge blanket reactor with no previous exposure to MC has acclimated to 20 mg/L MC after initial inhibition at 10 mg/L.