Sulfur amino acid intake in humans is variable and optimal SAA intake has not been adequately defined. The average American diet contains about 100 g of protein daily (4); the mean SAA intake is about 2.4 g (11). Daily intakes range from < 0.3 g to > 5 g (11). Most of the SAA is derived from animal protein, which constitutes about 2/3 of the total protein intake. The content of SAA in legumes and some types of nuts is about half of that in animal protein while most other plant-derived foods contain only 10-20% of the SAA found in an equivalent amount of animal protein. Because plant-derived foods are low in total protein, individuals who do not consume animal protein are at risk of SAA deficiency. Conversely, if excess SAA has associated health risks due to H2S or other toxic metabolites generated by colonic flora, individuals consuming diets high in animal protein would be at risk (12). Hence, Dietary Reference Intake values for SAA are needed as a foundation for improved dietary guidelines.