Latosol soils, red, dark red, red-yellow, and red-yellow treated with vinasse, were studied by microcalorimetry. Microbial activity was stimulated by the addition of identical masses of glucose with ammonium sulphate, varying from 3.0 to 12.0 mg per 1.5 g of soil (glucose being a limiting energy source) under controlled humidity at 298 and 306 K. After dosing all the soil samples (1.5 g) with 6.0 mg of each nutrient and 0.8 cm3 of water, the power-time curves were recorded. These curves showed that red soil gave the largest power output (240 mu W) at a peak time of 35.2 h (the point of maximum amplitude of the experimental curve). Yellow soils, however, did not show any response to addition of nutrients. The power-time curves are all similar in shape, with the thermic effect and the peak time for both temperatures being directly dependent on the amount of nutrient. The peak time decreases with increasing temperature; values of 29.2-43.8 h at 298 K and 17.3-23.8 h at 306 K, were obtained.