In intensive farming areas, the design of biological nitrogen removal plants for piggery wastewater requires the determination of the chemical oxygen demand (COD) fractions of the effluent. For this purpose, an experimental procedure was developed to quantify the inert soluble (SI) and particulate (XI) COD fractions, as well as the readily (SS) and the slowly (XS) biodegradable COD fractions. For the four wastewasters tested, the SI and the XI fractions were equal to 3-4 g O21-1 and 17-28 g O21-1, respectively, which resulted in a total inert fraction of 42-84% of total COD. The SS and the XS fractions were very variable, ranging 0-5 g O21-1 and 4-25 g O21-1 respectively, depending on the farm management practices and the storage conditions prior to biological treatment. From these results, the denitrification potential of the piggery wastewaters for biological nitrogen removal treatment could be assessed.