Microcosm studies determined that the indigenous microflora of the subsurface Groseclose clayey loam did not metabolize TBA, but TBA degradation was stimulated by the addition of the Pseudomonas sp., VT100. The indigenous subsurface microflora of the Fredrick clay metabolized TBA in soil microcosms that contained 10 to 500 mg/liter TBA. The addition of Pseudomonas sp., VT100, to the Fredrick clay enhanced the rate of TBA degradation in the l0 and 500 mg/liter TBA treatments, and reduced the time required for the initiation of TBA degradation. The indigenous Fredrick clay microflora reduced the growth and TBA degrading potential of the Pseudomonas sp. The addition of yeast extract and acetate to the Groseclose clayey loam allowed the indigenous microflora to initiate TBA degradation and enhanced TBA degradation in the sterile Groseclose clayey loam inoculated with Pseudomonas sp., VT100. We hypothesize that the native TBA-degrading microflora competed with the Pseudomonas sp. in both soils. A 1.0 mM molybdate amendment stimulated TBA degradation by the indigenous microflora but reduced the rate of TBA degradation by Pseudomonas sp., VT100, in subsurface soil microcosms. A TBA-degrading Alcaligenes sp. was isolated from the Fredrick clay. Limited TBA degradation was observed in one of three deep subsurface coastal plain soils after 220 days of incubation.