A facultative alkalophile capable of utilizing 4-chlorobenzoate (4-CBA), strain SB8, was isolated from soil with an alkaline medium (pH 10.0) containing the haloaromatic compound as the carbon source. The strain, identified as an Arthrobacter sp., showed rather extensive 4-CBA-degrading ability. 4-CBA utilization by the strain was possible in the alkaline medium containing up to 10 g of the compound per liter. The 4-CBA-dechlorinating activity of resting cells was almost completely uninhibited by substrate concentrations up to 150 mM. The bacterium dehalogenated 4-CBA in the initial stage of the degradation and metabolized the compound via 4-hydroxybenzoate and protocatechuate. O(2) was needed for 4-CBA dechlorination by resting cells but not by cell extracts. O(2) was inhibitory to the 4-CBA dechlorination activity of cell extracts. These facts suggest dechlorination of 4-CBA by halide hydrolysis and an energy requirement for the transport of 4-CBA into cells.