The investigators propose to conduct a community-based, double-blind randomized controlled trial in Mirpur area of Dhaka city. Adults aged 18 to 45 years residing in the catchment area for at least the last six months will be eligible for the study. A total of 440 subjects (220 females) will be enrolled. The results of the proposed study will contribute to our existing knowledge of the effect of lysine on incidence and severity of diarrheal illness as well as on immune status. A positive impact of lysine supplementation on diarrheal illness may lead to a future strategic approach to the control of diarrhea as a global public health problem.