The influence of dietary cellulose and indigestible dry matter on endogenous and metabolic faecal nitrogen excretion was studied. Adult colostomized Single Comb White Leghorn cockerels were used as experimental animals to collect urine and faeces quantitatively. The chickens were force-fed an equal amounts of a basal protein free diet (60g/d) with either varying levels of cellulose (0, 5, 10 and 15g/d) or added aluminium silicate (12g/d) for 8 days. Endogenous urinary nitrogen excretion was not influenced by cellulose intake nor by aluminium silicate intake. Each added increment of cellulose increased metabolic faecal nitrogen excretion. It was also shown that indigestible aluminium silicate increased metabolic faecal nitrogen. The additional loss of metabolic faecal nitrogen excretion in the droppings from large quantities of indigestible materials could be expected to increase protein requirement of chickens fed rations high in indigestible dry matter. However, there remains a possibility that the amount of food eaten itself increased MFN, since MFN excretion per g of food eaten was not altered with the increase of dietary cellulose or aluminium silicate.