BACKGROUND: Combustion at high temperature is a common treatment method for heavily contaminated soils. The capacity of the combustion process is negatively correlated with organic matter content of the soil. Thus, by reducing the amount of soil organic matter, batch size could be increased and the combustion process improved. In this study, the possibility to pre-treat soil containing high levels of organic matter with white-rot and litter-decomposing fungi was examined and scaled up. RESULTS: Calculations based on the CO2 production in laboratory experiments indicated that 20% of the soil organic carbon would have been degraded in 6 months when treated with Sphaerobolus stellatus and 10% when treated with Stropharia rugosoannulata. In a pilot-scale experiment with S. rugosoannulata mass loss due to degradation of soil organic matter accounted for 10% of the total weight of the soil in 6 months. CONCLUSION: A fungal pre-treatment process for contaminated soils with high organic matter content was developed. Good results were obtained with S. stellatus and S. rugosoannulata and the process was successfully scaled up to 300 kg scale. (C) 2009 Society of Chemical Industry