Prior to randomization the patient and clinician will determine whether the background therapy will be zidovudine (ZDV) plus lamivudine (3TC) or other background antiretroviral therapy (OBAT). Patients will then be randomized to IDV or matching placebo. AS PER AMENDMENT 06/27/97: The protocol was closed as of 03/25/97, and all patients have been unblinded to their assigned treatment. Patients still on study medication are eligible for the protocol extension. Patients who were randomized to immediate IDV may continue on therapy for up to an additional 4 months. All study therapy, both for those on immediate or delayed therapy, must be discontinued on 10/24/97.