The purpose of this study is to determine if treatment with an anti-HIV drug containing ritonavir and Agenerase is safe and can lower the level of HIV in the blood in patients who have failed an anti-HIV drug treatment containing nelfinavir.

HIV-infected patients will be treated with a ritonavir-enhanced Agenerase regimen.

Inclusion Criteria

Patients may be eligible for this study if they:

• Are 18 years of age or older.
• Are HIV-positive.
• Have a viral load (level of HIV in the body) of more than 1,000 copies/ml.
• Have had more than 12 weeks of prior anti-HIV drug treatment.
• Have failed a previous anti-HIV treatment containing nelfinavir as the only protease inhibitor.
• Are responsive to Agenerase.
• Are able to follow study requirements.

Exclusion Criteria

Patients will not be eligible for this study if they:

• Are intolerant to ritonavir (an anti-HIV drug).
• Have or have had problems with absorption.
• Have liver disease or damage.
• Have pancreatic disease or damage.
• Have taken any protease inhibitor other than nelfinavir.
• Are receiving investigational drugs or devices from another study.
• Are pregnant or breast-feeding.
• Currently use triazolam, astemizole, ergot medications, cisapride, midazolam, bepridil, rifampin, terfenadine, or pimozide.
• Have a bleeding disorder.
• Have previously been treated with Agenerase.
• Are receiving nonnucleosides.