The purpose of this study is to see if ABT-378/ritonavir plus efavirenz is safe and effective in lowering the amount of HIV in the blood of patients who have been treated with more than 1 protease inhibitor (PI).

All patients take ABT-378/ritonavir and efavirenz; there are no placebos in this study. Patients take study medications for 48 weeks, during which time there will be 15 study visits. There is a possibility of a study extension after 48 weeks.

Inclusion Criteria

Patients may be eligible for this study if they:

• Are HIV-positive.
• Have a viral load (level of HIV in the blood) of at least 1,000 copies/ml.
• Have been receiving stable (no changes) anti-HIV treatment that includes at least 1 PI for at least 8 weeks prior to study entry.
• Have received more than 1 PI for at least 12 weeks each at some time in the past.

Exclusion Criteria

Patients will not be eligible for this study if they:

• Have had any active opportunistic (AIDS-related) infections within the past 30 days.
• Have ever received nonnucleoside reverse transcriptase inhibitors (NNRTIs), such as delavirdine, nevirapine, or efavirenz.
• Have received certain medications.
• Are pregnant or breast-feeding.
• Abuse alcohol or drugs.