The objective of this study is to evaluate the safety and utility of bacteriophage phi X174 immunization as a tool to assess the immune competence of HIV-infected patients at different stages of disease in vivo, and to assess the impact of viral load levels and therapy-induced changes in viral load levels on the response to immunization with the neo-antigen bacteriophage phi X174. Bacteriophage phi X174 immunization is a method that has been in use for more than 25 years to assess the immunity of patients with various types of primary and secondary immunodeficiencies, including 48 HIV-infected patients. This is a prospective open-label, controlled study which will enroll 39 HIV-infected patients and 13 healthy volunteers, male or female with 18 years of age and over. The HIV-infected patients will be divided into 3 groups according to their CD4 cell count: less than 200 cells/mm(3), between 200 and 500 cells/mm(3) and greater than 500 cells/mm(3). After screening and a two week pre-study evaluation, all eligible participants will receive a primary, secondary and tertiary immunization with 2 x 10(9) PFU/kg of bacteriophage phi X174 six weeks apart. Patients who present with detectable levels of viral load at entry will be offered a more effective antiviral drug regimen. Patients will have to be on a stable antiviral regimen for at least one month prior to receiving the primary immunization. Patients will return for visits 1, 2 and 4 weeks after each immunization for clinical and laboratory evaluations. The study endpoints are: safety (as measured by incidence of adverse events, CD4 cell count and HIV plasma RNA), kinetics of bacteriophage clearance following primary immunization, quantitation of bacteriophage phi X174 specific antibody titers following primary, secondary and tertiary immunizations and determination of qualitative and quantitative antibody isotype switching following secondary and tertiary immunizations.