. Based on previous studies the investigators propose to perform a placebo-controlled double- blind study to define the role of bacterial overgrowth in children with HIV infection. It is also proposed to further define the molecular nature of HIV and other microbial agents shed in the stools of HIV-infected children with gastrointestinal abnormalities. The ultimate goal of these studies is the development of practical therapeutic regimens for the prevention and treatment of gastrointestinal dysfunction in HIV-infected infants and children.