Inclusion Criteria

Concurrent Medication:

Allowed:

- Antiretroviral regimen containing a protease inhibitor and one or two nucleoside reverse transcriptase inhibitors that has not changed in the last 12 weeks.

Patients must have:

- HIV infection with plasma HIV RNA of at least 1,000 copies/ml and less than or equal to 100,000 copies/ml at screening.

Prior Medication:

Allowed:

Naive to or has had less than 8 weeks of at least one nucleoside reverse transcriptase inhibitor and an acceptable regimen of two nucleoside reverse transcriptase inhibitors.

Exclusion Criteria

Concurrent Medication:

Excluded:

• Medications that are contraindicated with ABT-378/ritonavir for the duration of the study, such as midazolam, triazolam, terfenadine, astemizole, cisapride, pimozide, ergotamine and dihydroergotamine.
• Over-the-counter medicine or alcohol, without knowledge or permission of the investigator.

Patients with the following prior conditions are excluded:

• Evidence of acute illness determined by vital signs, physical examination, or laboratory results.
• Clinically significant abnormal ECG results.
• Positive test result for drug abuse with the exception of cannabis, unless the investigator anticipates cannabis use will interfere with compliance with the study.

Prior Medication:

Excluded:

• Investigational drugs with the exception of Amprenavir within 28 days prior to the initiation of study dosing.
• Treatment with a non-nucleoside reverse transcriptase inhibitor.
• Treatment with a protease inhibitor different from the current protease inhibitor for more than 6 weeks prior to current regimen.
• Treatment with more than one protease inhibitor concurrently.

Risk Behavior:

Excluded:

• Active substance abuse, alcohol abuse, psychiatric illness.
• Presumption, by investigator, of poor compliance to regimen.