A large number of patients with HIV infection have virus which has developed resistance to antiretrovirals, particularly protease inhibitors, resulting in treatment failure. Ritonavir has been increasingly used in combination with other protease inhibitors, including indinavir and lopinavir, because of its ability to improve plasma drug concentrations and prolong the half-life of other protease inhibitors. At the 1st International AIDS Society Conference on HIV Pathogenesis and Treatment [Buenos Aires, Argentina; July 2001], two studies reported the use of ritonavir as part of salvage therapy in patients with HIV infection. In the first study, patients who had experienced virological failure while receiving indinavir-based therapy achieved undetectable viral loads when ritonavir was added to their regimen. In the second study, response to multiple drug rescue therapy in heavily-pretreated patients was enhanced when lopinavir/ritonavir was part of the regimen. A third interesting study looked at the efficacy of PEG interferon (IFN)-α-2b in patients with HIV infection failing highly active antiretroviral therapy (HAART), and found that viral loads were decreased after 4 weeks, suggesting that this cytokine may have a therapeutic role in the treatment of such patients.