Inclusion Criteria

Children may be eligible for this study if they:

• Are HIV-positive.
• Are between 3 months and 16 years old (consent of parent or legal guardian required). (These age requirements reflect a change.)
• Have a plasma viral load of at least 400 copies/ml at screening.
• Agree to practice abstinence or use effective methods of birth control during the study.
• Are able to take oral medication and comply with study requirements.
• Are taking at least 1 nucleoside reverse transcriptase inhibitor (NRTI), such as zidovudine (ZDV) or stavudine (d4T). Patients can begin taking NRTIs at the beginning of the study.

Exclusion Criteria

Children will not be eligible for this study if they:

• Have had more than 2 episodes of moderate to severe diarrhea or vomiting lasting more than 4 days within 3 months prior to study entry.
• Are allergic to EFZ or NFV.
• Have any disease, including hepatitis, cancer, or an active opportunistic (HIV-associated) infection.
• Are pregnant or breast-feeding.
• Are taking any other experimental drugs or certain medications.
• Have ever taken protease inhibitors (PIs) or nonnucleoside reverse transcriptase inhibitors (NNRTIs).