A study was conducted using two duodenal and ileal cannulated, 45 kg gilts, to determine the bacterial amino acid contribution to amino acids in ileal digesta by using ³⁵S and diaminopimelic acid (DAPA) as bacterial protein markers. Both the ³⁵S and DAPA marker techniques are based on the assumption that a representative purified bacterial pellet is collected from ileal digesta samples. The ³⁵S technique was modified from previous methods by isolating a specific methionine sulphone marker fraction. However, results from the ³⁵S-methionine sulphone marker technique exceeded sensible physiological estimates (mean of 190.6%) of the bacterial amino acid contribution to ileal digesta amino acids. Whereas, the mean bacterial amino acid contribution to ileal digesta was 29.4% when determined using the DAPA marker technique. The values determined by DAPA are within the 20 to 34% range of values that have been reported for pigs fed cereal based diets. The amino acid composition was different (P≤0.05) between bacteria and undigested non-bacterial residues for isoleucine, aspartic acid, glycine, cysteine and tyrosine. The high concentration of glycine in non-bacterial residues relative to other amino acids measured and the corresponding low concentration in bacterial samples suggests that the bacterial pellet fraction was free of contamination. It was therefore concluded, that further research into determining the bacterial contribution to amino acids in ileal digesta is warranted.