Calorimetric and respirometric studies of the decomposition of animal wastewaters (AWW) in soil at 298.20 K were carried out. A high-volume differential calorimeter (0.5 dm(3)) and an electrolytical respirometer were used for separate measurements. The AWW were sampled from a pig-fattening farm. The soil was supplemented with different doses of AWW corresponding to 20, 40, 60 and 80 mg N per 100 g of soil. The heat production rates, total heat effects and the apparent rate constant were determined. The comparative respirometric measurements confirmed that the processes that were investigated calorimetrically are largely aerobic.