Triple-drug antiretroviral regimens have become the recommended approach to therapy for HIV infection. [AS PER AMENDMENT 12/4/00: The clinical use of multiple-drug antiretroviral regimens containing various combinations of nucleoside reverse transcriptase inhibitors (NRTIs), nonnucleoside reverse transcriptase inhibitors (NNRTIs), and protease inhibitors (PIs) has become a widespread approach to therapy for HIV infection, especially for patients previously treated with PIs.] Since the introduction of PIs, a greater awareness of the relationship between optimal suppression of viral replication, genotypic resistance, and viral rebound has led to the design of more potent antiretroviral drug combinations. Two ACTG clinical trials addressing the issue of virologic failure utilize antiviral regimens that include 2 NRTIs, 2 PIs (one of which is APV), and EFV (NNRTI). Although this drug combination is logical, there is limited PK data to guide the dosing selection. This study enrolls healthy volunteers to obtain PK profiles and metabolic assessments of APV/EFV before and after the addition of a second PI [AS PER AMENDMENT 12/4/00: APV alone, APV combined with EFV, and APV/EFV combined with a second PI].