Comparative studies on the effects of casein, urea and poultry waste on the fermentation of starch and cellulose were conducted. Incubation of starch with poultry waste for 390 min resulted in greater overall gas, total VFA and ammonia production than in control incubations (grass cubes and hay). Between 210 and 390 min the ammonia concentration fell, indicating microbial utilisation of nitrogen. Replacement of poultry waste with casein resulted in lower gas and total VFA production and similar ammonia concentrations in comparison with the control incubation. When starch was incubated with urea, the ammonia concentration rose rapidly, causing an elevated pH and poor VFA production. When cellulose was incubated with any of the three nitrogen sources, gas and total VFA production were considerably lower than in control incubations. Inclusion of urea as a nitrogen source had an effect on cellulose fermentation similar to that seen with starch. When grass cubes and hay were incubated with poultry waste, gas production was similar to that of the control; however, ammonia and total VFA production were greater than in the control. The results indicate that the carbohydrate content of poultry waste may be useful in promoting the establishment of fermentation, and that the slow release of ammonia may facilitate a more efficient fermentation of roughage in nutrients such as grass and hay.