On Kwajalein Island in the Republic of the Marshall Islands, studies were conducted to characterize subsurface petroleum contamination and assess the potential for bioremediation of contaminated soils and sediments. Because of its remote location and problems with shipment of sample materials off-site, characterization and biotreatability studies were conducted on the Island during a 12-d site visit. Analyses were made of soil contamination levels, physical/chemical properties, and microbial densities, while microcosm studies were made of biodegradation potential. It was found that the coral-derived sands on Kwajalein Island were alkaline (e.g., pH > 8) and deficient in nutrients (e.g., low N, P). Microorganisms were abundant (103-107 org.g(-1)) and included appreciable hydrocarbon degraders. Diesel fuel contamination ranged from below detection limits to nearly 9000 mg TPH kg(-1), with the highest levels in the capillary fringe and upper saturated zone of a freshwater lens beneath the Island. Biodegradation of fresh diesel fuel added to clean soil occurred very slowly (e.g., < 0.5 mg TPH kg(-1) d(-1)). Biodegradation of diesel fuel added to previously contaminated soils that were also supplemented with nutrients, proceeded at higher but still relatively low rates (e.g., < 2 mg TPH kg(-1) d(-1)). It was concluded that bioremediation of diesel fuel contaminated soils by indigenous organisms was feasible on Kwajalein Island, although degradation rates were very low, with some enhancement possible by the addition of nutrients.