Study 006 is a pivotal Phase III, multicentre, randomized, open-label study designed to compare the antiretroviral activity and tolerability of efavirenz (EFV) + zidovudine (AZT) + lamivudine (3TC) with indinavir (IDV) + AZT + 3TC and EFV + IDV. Using both the 'observed data' analysis and intent-to-treat non-completer = failure analysis, the results at 48 weeks showed that efavirenz, in combination with AZT + 3TC was superior to IDV + AZT + 3TC. EFV + AZT + IDV was shown to be equally effective in patients with high and low baseline viral loads. Toxicities resulting in premature discontinuations were 3-fold higher in the IDV + AZT + 3TC arm than in both efavirenz-containing arms. Preliminary results suggested that efavirenz increased high density lipid (HDL) levels but the clinical significance of this observation is unknown. The results from Study 006 indicate that the combination EFV + AZT + 3TC is a highly active protease inhibitor-sparing regimen for first-line treatment of HIV-infected patients.