Microbial fuel cells (MFCs) are a device using microorganisms as biocatalysts for transforming chemical energy into bioelectricity. As soil is an environment with the highest number of microorganisms and diversity, we hypothesized that it should have the potential for energy generation. The soil used for the study was Mollic Gleysol collected from the surface layer (0-20 cm). Four combinations of soil MFC differing from each other in humidity (full water holding capacity [WHC] and flooding) and the carbon source (glucose and straw) were constructed. Voltage (mV) and current intensity (mu A) produced by the MFCs were recorded every day or at 2-day intervals. The fastest and the most effective MFCs in voltage generation (372.2 +/- 5 mV) were those constructed on the basis of glucose (MFC-G). The efficiency of straw MFCs (MFC-S) was noticeable after 2 weeks (319.3 +/- 4 mV). Maximal power density (P (max) = 32 mW m(-2)) was achieved by the MFC-G at current density (CD) of 100 mA m(-2). Much lower values of P (max) (10.6-10.8 mW m(-2)) were noted in the MFC-S at CD of ca. 60-80 mA m(-2). Consequently, soil has potential for production of renewable energy.