Volunteers are randomized to one of four groups. Group I receives vCP205. Group II receives vCP1433. Group III receives vCP1452. Group IV receives an ALVAC rabies vaccine, as a control. Immunizations are administered at Months 0, 1, 3, and 6. At Months 3 and 6, patients in Groups I, II, and III also receive gp160 MN/LAI-2, the subunit boost vaccine. Group IV receives another placebo vaccine. Participants have regular clinic visits and blood is drawn to determine humoral and cellular immune responses to the vaccines. [AS PER AMENDMENT 10/23/98: A cell-mediated immunity substudy has been added at selected institutions following the fourth vaccination at 6 months; this study will assess the newer assays of CD8+ T cells and the kinetic response following immunization. The 6-month immunization may be rescheduled by up to 14 days to accommodate clinical, laboratory, or volunteer scheduling issues.] [AS PER AMENDMENT 6/17/99: Three study arms are added. Group V receives vCP1452 at Months 0,1,3, and 6. Group VI receives vCP205 at Months 0,1,3, and 6. Group VII receives placebo at Months 0,1,3, and 6. Patients in Groups V, VI, and VII do not receive the subunit boost, gp160 MN/LAI-2. Consenting volunteers enrolled in the three new groups at Johns Hopkins University undergo PET scanning as part of an ancillary study.]