OBJECTIVE: To examine the use of low-dose ritonavir as a pharmacokinetic enhancer for HIV protease inhibitors. DATA SOURCES: Primary articles, review articles, and conference abstracts identified by MEDLINE search (1995–May 2001) and secondary sources. DATA SYNTHESIS: Low-dose ritonavir (100–200 mg) is increasingly being combined with HIV protease inhibitors to improve their effectiveness and allow less frequent dosing. An evaluation of the clinical evidence supporting this practice was conducted. CONCLUSIONS: Limited outcome data exist for low-dose ritonavir-based regimens in general. Although preliminary data appear promising, more clinical evidence is needed to determine the optimal dosing, long-term safety, and relative effectiveness of this approach. The role of these regimens in early therapy remains to be defined.