Poultry litter is composted to reduce odor and pathogens and to improve its quality as a soil amendment. Organic material, e.g., sawdust, is added to increase the C:N ratio to achieve optimum degradation of organic C and retention of N through microbial biomass formation. However, the relative biodegradabilities of the organic material in poultry litter and the amendment are usually not known. Furthermore, it is assumed that as microorganisms metabolize organic compounds and produce CO2, they increase in biomass and, therefore, retain N. In this study, bench-scale compost reactors were used to determine the relative contributions of poultry litter and of the amendment (sawdust) to the biodegradability of a compost mix. Approximately 29% of the volatiles lost from the poultry litter mix came from the sawdust. Fiber analyses revealed that only a small portion of cellulose was degraded. Although microbial subpopulations able to degrade selected macromolecules were present at varying levels, the overall level of microorganisms did not change markedly. Populations capable of degrading bacterial cell walls were present throughout the composting period, and microbiological assays indicated that inorganic nutrients were available to support limited microbial growth. These results suggest that N compounds and inorganic nutrients are recycled, rather than fixed during composting.