Commercial production of products from nanomaterials, such as fullerenes, will result in an inevitable release of these materials as spills or as a part of waste streams that may enter soil. At present, virtually no data exists on the effect of these nanomaterials on soil microbial populations.  The impact on soil systems should be considered as other studies have indicated a toxic effect of fullerene materials on both prokaryotic and eukaryotic organisms in other matricies.  In this study, the application of fullerene (C60), an aqueous dispersion of C60 (nC60) and graphite (C12) to soils was studied over a 2 month period by measuring the microbial activity as indicated by respiration of an added substrate.  We also evaluated the effects of an environmental stressor on the responses to the applied carbon materials by adjusting and maintaining the soils at different water potentials.  At weekly intervals, microbial respiration was measured by treating subsamples with ¹⁴C-glucose and assaying for evolved ¹⁴C-CO₂.  At the termination of the experiment, phosphospholipid fatty acids (PLFA) were extracted and analyzed to assess any differences in the size or composition of the microbial populations.  Respiration data showed that the effect of the application of carbon materials tended to decrease respiration but only slightly.  PLFA data showed little change in the soil community structure.