A contaminated area situated at Eppelheim (Germany) is a dump for volatile hydrocarbons wastes [mainly perchloroethylene (PCE); benzene, toluene, ethylbenzene and xylene (BTEX-aromatics)]. The present work was carried out to investigate the efficiency of indigenous soil microorganisms present in successive soil layers up to 8 m to degrade PCE and toluene under anaerobic and aerobic conditions, respectively. The incorporation of carbon from PCE or toluene into cell mass of indigenous soil microorganisms was studied as well. PCE was completely dechlorinated via reductive dechlorination within 56 days of incubation. Two patterns of dechlorination, depending on soil depth, could be distinguished: (i) PCE--> trichloroethylene (TCE) --> cis-1,2-dichloroethylene (cisDCE) --> vinyl chloride (VC) --> ethane [unpolluted upper soil] and (ii) PCE--> TCE--> cisDCE [moderately pollted lower soil], suggesting that two different anaerobic metabolic microbial groups participated in the dechlorination process. Experiments with ¹⁴C-[1,2]-PCE indicated that [¹⁴C]ethane was the principal product of biodegradation in unpolluted upper soil reaching up to 75.9 %. On the other hand, in moderately polluted lower soil the major biodegradation products were ¹⁴C-less-chlorinated hydrocarbons but not ¹⁴C-ethane. ¹⁴CO₂ and ¹⁴CH₄ were observed in only low concentrations (2.2 to 9.6 % and 0.0 to 5.0 %, respectively). However, the production of ¹⁴CO₂ from [¹⁴C]PCE indicated that at least partial mineralization of PCE could occur. The assimilated PCE-C in the cell mass accounted only for 0.4 to 4.4 %, indicating that soil microorganisms were unable to use PCE as a growth substrate. Experiments with [¹⁴C]-uniform-toluene demonstrated that toluene was biologically mineralized in all soil depths with different ratios. Indeginous soil microorganisms converted toluene to CO₂ (45.5 - 60.4 %) and cellular material (16.0 - 27.7 %). This relatively high percentage of radioactive biomass formation indicated that toluene was assimilated by the soil microorganisms as an energy and carbon substrate. The ¹⁴CO₂ formation activities ranged between 0.074 and 0.183 mg ¹⁴CO₂-C/kg soil dry wt. h^-1 and were ca. 4.4 times lower than the corresponding elimination of unlabelled toluene (0.17 and 0.93 mg toluene-C/ kg soil dry wt. h^-1).