The microbial ecology of pristine and contaminated ground water at a chemical waste disposal site was investigated. Recently, it was determined that ground water downslope from the disposal site contained elevated levels of toxic pollutants, including benzene, toluene, xylene and methylene chloride, as well as iron and manganese. Microbial mineralization and uptake of radio-labeled glucose and amino acids indicated a metabolically active microflora in both pristine (upslope from the contamination) and contaminated groundwater samples collected from monitoring wells at the site. However, microbial uptake and mineralization of glucose and amino acids were up to fourfold slower in the contaminated well water than in the control well. Rates of mineralization and uptake of toluene were easily measurable in water from the contaminated but were negligible in water from the pristine well, suggesting that the subsurface microflora in the contaminated region had adapted to degrade toluene. Additions of the inorganic nutrients N, K, and P enhanced toluene mineralization in water from the contaminated well, with the addition of K and P enhancing mineralization twofold. The addition of these inorganic nutrients, therefore, presents an opportunity for biorestoration of the site. An increase in the incubation temperature also enhanced toluene mineralization; however manipulation of pH and dissolved oxygen concentration had no measureable effects.