Active Immunization of HIV-1 Infected, Pregnant Women With CD4 Lymphocyte Counts >= 400/mm3: A Phase I Study of Safety and Immunogenicity of MN rgp120/HIV-1 Vaccine (NOTE: Some Patients Receive Placebo)

Inclusion Criteria Concurrent Medication: Allowed: AZT. Acyclovir. Patients must have: HIV-1 infection. CD4 count >= 400 cells/mm3. No AIDS-defining illness or other systemic manifestations related to HIV (other than generalized lymphadenopathy). HIV p24 < 30 pg/ml. Proven pregnancy in the 16th to 24th week of gestation at study entry, with no special obstetrical risks. Concurrent AZT therapy is permitted. Exclusion Criteria Co-existing Condition: Patients with the following symptoms and conditions are excluded: Known hypersensitivity to a component of the vaccine. Evidence of fetal abnormality on ultrasound. Evidence of maternal risk factors including insulin-dependent diabetes, moderate to severe hypertension, repeated fetal wastage (> 3), Rh-sensitization or other blood group alloimmunization, severe renal disease, previous infants with malformations or other factors that obstetrically are judged to constitute a special risk of spontaneous abortion or premature birth. Active syphilis. Hepatitis B surface antigen positive. Concurrent Medication: Excluded: Antiretroviral or immunomodulating agent other than AZT during the pregnancy. Prior Medication: Excluded: Antiretroviral or immunomodulating agent other than AZT within 90 days prior to study entry. Current use of illicit drugs or known chronic alcohol use.