ORIGINAL DESIGN: To evaluate the clinical and immunologic safety of MN rgp120/HIV-1 vaccine (MN rgp120 vaccine) given alone or concurrently with the IIIB rgp120/HIV-1 vaccine (IIIB rgp120 vaccine) in healthy HIV-1 seronegative adult subjects. To compare the immune response to MN rgp120 vaccine given at 100, 300, or 600 mcg. To determine the immune response to 300 mcg MN rgp120 vaccine and 300 mcg IIIB rgp120 vaccine given concurrently.