Laboratory bioremediation experiments were performed with soil from a diesel-oil contaminated waste disposal site; contamination was 5580 mg hydrocarbons per kg soil dry mass. The effects of incubation temperatures (10 degrees C and 25 degrees C), of the addition of an inorganic fertilizer at C : N ratios of 10 : 1 and 50 : 1, of the indigenous soil microorganisms and of a psychrotrophic and a mesophilic inoculum capable of degrading diesel-oil were investigated. The highest diesel-oil decontamination rates were 43% at 10 degrees C and 55% at 25 degrees C after 30 days. The biodegradation activity of the indigenous soil microorganisms was highly increased by the use of fertilizers. The diesel-oil degradation activity of the added inocula was highest when no fertilizer was present and was inhibited by nutrient supply. Abiotic processes did not contribute to diesel-oil elimination.