Quantitative determination of hydrochlorothiazide (HCTZ) and candesartan (CDS) in human plasma in volunteers was performed using a sensitive, selective and specific LC-MS method which has been developed and validated before the study. The study was performed by means of a liquid chromatograph Shimadzu Prominence equipped with a mass spectrometer LCMS-2020. Analytical column PerfectBond ODS-HD HPLC-column 5 µm 250 × 3.0 mm with a pre-column cartridge PerfectBond ODS-HD 5 µm 10 × 3.0 mm, double source of ionization for LCMS-2020 (electrospray (ESI) and chemical (APCI)) and software LabSol LCMS V5 LCMS2020 systempack were used. The low limit of the quantitative determination for HCTZ and CDS made up 10 ng/ml. m/z for CDS 441.20-positive scan, m/z for HCTZ 295.90-negative scan. The method has been applied to a pharmacokinetic study of 12.5 mg HCTZ and 16 mg CDS tablet in healthy volunteers.