The efficient production of the weaner pig requires accurate knowledge of its amino acid requirements. This is particularly relevant today as it is increasingly important to reduce nitrogenous waste from pigs. During the past decade formulations for feeds were based on the ideal protein profile of the lean tissue of pigs in which the sulphur amino acid requirements were assessed as the combination of total sulphur amino acids rather than through their individual amino acids, methionine and cystine (Agricultural Research Council, 1981). Today, this concept is challenged. The effect of the changing cystine demand in the weaner pig on the total ileal digestible sulphur amino acid (IDSAA) requirements and hence methionine levels requires study. The objective of this experiment was to understand the requirements and relationship between true ileal digestible cystine and methionine to lysine ratio in the ideal protein content of food to achieve efficient production in the young pig.