Recent research has shown that the bioremediation of oil-polluted soil by activation of microflora is not always advantageous when compared with the introduction of oil degrading microorganisms. Although microflora isolated from oil-polluted sites is adapted for growth under the above conditions, this does not imply a high rate of oil degradation. Indeed, it has been shown that the hydrocarbon-oxidative activity of isolated strains to black oil was 13.1-17.3% (incubation for 10 days at 24degreesC), while the activity of a mixture of three aboriginal strains was 17.8%. At the same time, the hydrocarbon-oxidative activity of associations of the strains isolated from other regions was 24.0-30.0% (in 10 days). (C) 2003 Elsevier Ltd. All rights reserved.