A Study of Dryvax Vaccine Against Smallpox in Previously Unvaccinated Adults

Inclusion Criteria: Patients may be eligible for this study if they: * Are between 18 and 32 years of age. * Give written informed consent. * Are available for follow-up for 2.5 months. * Have an acceptable medical history by screening evaluation and brief clinical assessment. * Are HIV-negative. * Agree to use acceptable contraception and to not get pregnant during the study. Exclusion Criteria: Patients may not be eligible for this study if they: * Have a suppressed immune system. * Have participated in an HIV vaccine trial. * Have liver disease, diabetes, or kidney problems. * Have malignant skin cancer. * Have autoimmune disease. * Have used medication that suppresses the immune system. * Have had psychiatric or medical problems or have job responsibilites that will keep them from participating in the study. * Use illegal intravenous drugs. * Have received any live vaccines within 60 days of study start. * Have used experimental therapies within 30 days before study start. * Have been vaccinated with certain experimental vaccines. * Have a vaccination scar but have no record of having a vaccine. * Have received a smallpox vaccine. * Have taken blood products or immunoglobulin in the past 6 months. * Have a fever on the day of vaccination. * Have certain skin disorders, including eczema, exfoliative skin, lacerations that require stitches or burns larger than 2 x 2 cm. * Live with, have sexual contact with, or work with anyone who is pregnant, less than a year old, has eczema, has certain skin disorders, has a disease or takes medication that suppresses the immune system. * Have a condition that, in the opinion of the investigator, might interfere with the study. * Are allergic to any parts of the vaccine. * Are allergic to thimerosal, immunoglobulins, cidofovir, or probenecid. * Are pregnant or breast feeding.