Group A- ALVAC vCP205 plus SF-2 rgp120 in MF59. Group B- ALVAC vCP205 plus saline placebo. Group C- Placebo-ALVAC plus saline placebo. [AS PER AMENDMENT 7/2/98: Beginning 12-18 months after initial vaccination, then 2, 6, and 12 months later, 10 volunteers from group A receive saline placebo, while 50 volunteers each from groups B and C are rerandomized within their respective groups, and are treated as follows.