The objective of this study was to examine the possibility of measuring the growth of three white-rot fungi in soil contaminated with polycyclic aromatic hydrocarbons (PAHs), by estimating the soil levels of the phospholipid fatty acid (PLFA) 18.2 omega 6,9. The effect of the fungi on the PAH concentration and on the indigenous bacterial population in the soil was monitored. As shown by visual examination, the fungi investigated, Pleurotus ostreatus, Phanerochaete chrysoporium and Hypholoma fasciculare, grew well in autoclaved soil, whilst only H. fasciculare grew in non-autoclaved soil. In these reactors, there was also detected an increase in the PLFA 18.2 omega 6,9. However, the interpretation of the PLFA data was somewhat disturbed since 18:2 omega 6,9 also was found to be present in the birch wood used as a fungal substrate. In autoclaved soil, P. ostreatus and P. chrysosporium were found to exhibit a PAH degrading capability, with the total PAH concentration decreasing from 209 +/- 35 and 186 +/- 2 to 149 +/- 6 and 109 +/- 6 mg/kg dry weight (dw) soil, respectively, during the 10 week incubation period. No PAM-degradation could be detected in any treatment using non-autoclaved soil. In the autoclaved soil, the total level of bacterial specific PLFAs in all fungal treatments, and in a control using added ground birch sticks, was found to be lowered. In the non-autoclaved soil, 6 out of 9 selected bacterial PLFAs exhibited a significant change between the treatments, but the overall total content of bacterial PLFAs did not change. The present study has shown that it is possible to measure fungal growth in a PAH-contaminated soil derived from a former gasworks plant by estimating the levels of the PLFA 18:2 omega 6,9. The inoculated fungi affected the indigenous bacteria, as shown by estimating the level of bacterial specific PLFAs. Finally, fungal PAM-degradation could be detected in autoclaved soil but not in non-autoclaved soil.