Recent animal studies indicate that immunizing with MN rsgp120/HIV-1 in combination with QS21 on a 0, 1, 2 month schedule results in a more rapid rise in binding and neutralizing antibody response than on a 0, 1, 6 month schedule. Such an effect may be particularly desirable in vaccine delivery. This study compares these two delivery schedules using the unadjuvanted vaccine formulation rsgp120/HIV-1 with or without addition of alum.