The purpose of this study is to see if it is safe and effective to give adefovir (a new anti-HIV drug) plus nelfinavir to HIV-infected children who are already receiving other anti-HIV medications.

During the first phase of the study (Days 1-6), the safety and tolerability of multiple doses of ADF is assessed when administered simultaneously with the patient's reverse transcriptase inhibitor (RTI) regimen. The second phase begins on Day 7 when nelfinavir is added to the therapy regimen for an additional 15 weeks. ADF pharmacokinetics are measured on Days 1, 2, and 7 (on a subset of 18 patients); peak and trough samples are collected on Day 28.

Inclusion Criteria

Your child may be eligible for this study if he/she:

• Is 3 months to 16 years old.
• Is HIV-positive.
• Has never taken protease inhibitors or has previously taken ritonavir (RTV), saquinavir (SQV), or indinavir (IDV) and is willing to stop the medication at study entry.
• Is taking an anti-HIV drug combination that will not change during at least the 2 weeks prior to study entry.
• Agrees to use effective barrier methods of birth control, such as condoms, during the study.
• Has consent of parent or guardian.

Exclusion Criteria

Your child will not be eligible for this study if he/she:

• Has ever taken NFV.
• Has a history of opportunistic (AIDS-related) infection.
• Has any disease or illness that would prevent him/her from completing the study, including cancer.
• Has taken certain medications, including protease inhibitors at study entry.
• Is receiving an HIV vaccine at study entry.
• Is pregnant.