A new, simple, high throughput and accurate LC-ESI-MS has been validated for determination of saquinavir in human plasma by using doxepine as internal standard. The analyte and internal standard were detected with no interference in multiple reaction monitoring (MRM) in positive mode on an electrospray ionization-mass spectrometer on a LUNA 3μ, C18 (2), 100A, 100 X 4.60 mm column using a mobile phase of a buffer: Acetonitrile (20:80, V/V). The flow rate was 1 ml/min at the column temperature 40 ± 3 ºC. In these chromatographic conditions, the retention times of saquinavir and doxepine were found to be 1.37 min and 1.28 min respectively. The analytes were showed good linearity over a wide concentration range. The analyte and internal standard were stable in standard solution and in plasma samples under storage and processing conditions. The present work was fully developed and validated according to acceptance criteria for bioanalytical method validation
