A Randomized Double-Blind Control-Comparison Crossover Trial of Oral Glutamine to Suppress Frequently Recurrent Herpes Labialis

Background: * A cold sore is usually a blistering rash on or near the lips, caused by infection with herpes simplex virus. After the first infection, the virus goes into a dormant (inactive) state, but it can continue to cause cold sores. * Most people with the herpes simplex virus have a few episodes of cold sores per year. However, some individuals may have many recurrent episodes that are uncomfortable and may cause embarrassment. Researchers are attempting to find treatments that can decrease the number of cold sore episodes for people who have six or more episodes per year. * Glutamine is a molecule called an amino acid and is one of the components that make up proteins in the body. Clinical studies using glutamine have addressed the potential of glutamine to improve immune function and to heal damaged tissue or to help healing. Objectives: \- To find out if the dietary supplement glutamine can help individuals with frequently recurring (more than six episodes per year) cold sores. Eligibility: * Patients between 18 and 65 years of age who have a history of having six or more cold sore episodes per year, and have not received certain kinds of drug treatment for the cold sores within 1 month of beginning the study. * Patients who have two or more episodes of cold sores caused by the herpes simplex virus will be eligible for treatment as part of this study. Design: * Initial clinical visit for a physical examination and medical history, at which blood samples will be drawn for testing. * Eligible participants will undergo a 4-month screening period. Patients who develop sores during this period will visit the NIH to have the sore examined to determine if it is caused by the herpes virus. Patients who have two or more episodes of cold sores caused by the herpes simplex virus will be eligible for treatment. * Patients who are eligible for treatment will provide an initial blood sample and will receive randomized doses of either glutamine or glycine (another