Objective: We studied the relationships between plasma and saliva concentrations of antiretroviral drugs to explore whether saliva can be used for therapeutic drug monitoring (TDM). Methods: Abacavir (ABC), tenofovir (TFV), darunavir (DRV), and raltegravir (RAL) in plasma and saliva from 30 HIV-1-infected patients were quantified using liquid chromatography-tandem mass spectrometry. Results: Mean saliva-to-plasma concentration ratios were 0.623 (ABC), 0.024 (TFV), 0.065 (DRV), and 0.0135 (RAL), which agree with the plasma protein binding rates except TFV. Significant correlations were evident between saliva and plasma concentrations of ABC, DRV, and RAL. Conclusions: This study suggests that plasma concentrations of ABC, DRV, and RAL can be estimated from their saliva concentrations and that the saliva concentration of some antiretroviral drugs reflects the unbound drug concentration in plasma.