The proposed study will observe the impact of a daily dose of 2000 mg supplemental L-lysine for 6 months on diarrheal illness in an adult population of an urban slum area in Dhaka whose principal diet is based on cereals such as rice and or wheat. The daily protein and lysine availability from diets of Bangladeshi population has been calculated to be about 43g and 1883 mg respectively, compared to 113g and 7,598 mg respectively in the USA. This means that 2000 mg daily supplementation of L-lysine would not pose any detrimental effect, as the combined usual and supplemental intake will still be substantially lower compared to the intake in USA. However, as expected, the supplemental L-lysine may reduce the incidence and severity of diarrheal illness through improvement of the nutritional and immunological status of the study population.