3. Subsequently, all children who are able to tolerate the combination of zidovudine and lamivudine (i.e., have no prior history of intolerance to one of these two agents) will be treated with these two reverse transcriptase inhibitors in addition to the protease inhibitor indinavir. Zidovudine and lamivudine will be added after 16 weeks at a fixed dosage. Toxicity, pharmacokinetics, and preliminary efficacy of indinavir will also be investigated after combination therapy. All patients who wish to remain in this study after 96 weeks of therapy and who do not meet off study criteria will be permitted to receive extended treatment with their current indinavir combination therapy for an additional 48 weeks. The study will determine the pharmacokinetic profile of indinavir, given as single drug or in combination with zidovudine and lamivudine. It will assess the preliminary antiviral and clinical activity by monitoring clinical status, viral burden in plasma, and markers of immunologic status. Based on safety and preliminary efficacy results from studies performed in adults, we will study three dose levels which are expected to result in drug levels above the IC95 of HIV-1 for all or most of the dosing interval.