The aim of the investigation was to study the effects of lysine, methionine, crude protein, a complete balanced diet, maize starch and potato starch infused continuously into the caecum on the digestibility of the nutrients, urinary nitrogen excretion and N balance in the presence of a normal or a depressed (modified) microflora. 2. The effects of the the infused nutrients on digestibility differed when diets supplemented with antibiotics were compared with unsupplemented diets. 3. Infused lysine improved the digestibility of crude protein (0.004/g lysine), crude fibre (0.01/g lysine), gross energy (0.003/g lysine) and lysine (0.03/g lysine) when the diets were not supplemented with antibiotics. 4. Infused lysine, methionine and crude protein seemed to be of very little value for protein synthesis in the pigs, as the effects on N balance, although positive, were very small. 5. Despite the fact that a part of the infused lysine passed through the caecum-colon and into the faeces intact, the effect of N balance was negligible, indicating that the ability to absorb amino acids through the gut wall in the caecum-colon was very poor. 6. Crude protein, a complete balanced diet, maize starch and potato starch infused into the caecum were digested almost as well as if they had been given orally, thus demonstrating the large digestive capacity of the caecum-colon.
