A sensitive, specific and selective method has been developed for the simultaneous determination of bisoprolol and hydrochlorothiazide in human plasma. The method employed a state of the art LC-MS/MS operated in the positive and negative ionization switching modes. A simple sample preparation step involving protein precipitation with acetonitrile has been optimized; the analytes and the internal standard moxifloxacin were separated on a Purosphere STAR C8 column (125 mm x 4 mm, 5 microm). The mobile phase was an ammonium acetate solution (1 mM) with formic acid (0.2%): methanol and acetonitrile (65:17.5:17.5, v/v/v (%)), the flow rate was set at 0.65 mL/min. Bisoprolol and hydrochlorothiazide were ionized using ESI source prior to detection by Multiple Reaction Monitoring (MRM) mode while monitoring at the following transitions: positive m/z 326-->116 for bisoprolol, negative m/z 296-->269 and m/z 296-->205 for hydrochlorothiazide. Linearity was demonstrated over the concentration range 0.10-30.0 (ng/mL) for bisoprolol and 1.00-80.00 ng/mL for hydrochlorothiazide. The limits of detection were 0.100 (ng/mL) for bisoprolol and 1.00 (ng/mL) for hydrochlorothiazide. The validated method was successfully applied to a pharmacokinetic study of 5 mg bisoprolol fumarate with 12.5 mg hydrochlorothiazide tablet in healthy volunteers.