We recently reported the lysine requirement of school-aged children living in Canada consuming a mixed diet to be 35 mg.kg(-1).d(-1). Because the majority of children in the world live on cereal-based diets in developing countries, we measured the daily lysine requirement in healthy children living in India and consuming a mostly cereal-based diet. Our objective in this study was to determine the lysine requirement in healthy, school-aged children in the developing world by using the indicator amino acid oxidation method with l-[1-(13)C] phenylalanine. Six healthy, school-aged children consumed 7 levels of lysine (5, 15, 25, 35, 50, 65, and 80 mg.kg(-1).d(-1)) each in a random order along with an amino acid mixture providing energy and protein intakes of 1.7 x resting energy expenditure and 1.5 g.kg(-1).d(-1), respectively. The mean lysine requirement was determined by applying a 2-phase linear regression crossover analysis on tracer oxidation (F(13)CO(2)) data, which identified a breakpoint (requirement) at minimal F(13)CO(2) in response to the graded lysine intakes. The mean lysine requirements with the upper 95% CI for children were determined to be 33.5 and 46.6 mg.kg(-1).d(-1), respectively, by breakpoint analysis of the F(13)CO(2) data. The mean lysine requirements of Indian children were almost identical to that of Canadian children (35 mg.kg(-1).d(-1)). There is no evidence for any adaptation in lysine requirements in children from developing countries such as India.