In Part A, 28 healthy volunteers (15 vaccinia-immune and 13 vaccinia-naive) are randomized to receive intramuscular injections of ALVAC gp160 MN at a dose of 1 million TCID50 or ALVAC rabies glycoprotein as a control at months 0 and 2. In Part B, 90 healthy volunteers (60 vaccinia immune and 30 vaccinia naive) are randomized to receive ALVAC gp160 MN at a dose of 10 million TCID50 or ALVAC rabies glycoprotein control, on an immunization schedule of either month 0 and 1 or 0 and 2. For Part B, half of the patients receiving ALVAC gp160 MN, as well as approximately half of those receiving control vaccine, will receive booster immunizations with SF-2 rgp120 subunit protein, if available, at months 9 and 12; the other half will receive booster immunizations with the same preparation as they received for their first two immunizations. In Part A, all control volunteers except one within each control group receive SF-2 rgp120 subunit protein at months 9 and 12. An additional group of 10 volunteers will receive four injections of SF-2 rgp120 subunit protein at months 0, 1, 6 and 12. Part B will begin whenever the higher dose of ALVAC gp160 MN becomes available (at least 4 weeks after initiation of Part A). Volunteers are followed for at least 18 months. Per 06/10/94 addendum, volunteers will be contacted once or twice per year for at least 5 years to check on health status.