A rapid, sensitive and specific method to quantify carvedilol in human plasma using metoprolol as the internal standard (IS) is described. The analyte and the IS were extracted from plasma by liquid-liquid extraction using a diethyl-ether solvent. After removed and dried the organic phase, the extracts were reconstituted with a fixed volume of acetonitrile-water (50/50; v/v). The extracts were analyzed by a high performance liquid chromatography coupled to electrospray tandem mass spectrometry (HPLC-MS/MS). Chromatography was performed isocratically on Alltech Prevail C18 5 microm analytical column, (150 mm x 4.6 mm i.d.). The method had a chromatographic run time of 3.5 min and a linear calibration curve over the range 0.1-200 ng ml(-1) (r2>0.997992). The limit of quantification was 0.1 ng ml(-1). This HPLC-MS/MS procedure was used to assess the bioequivalence of two carvedilol 25 mg tablet formulations (carvedilol test formulation from Laboratórios Biosintética Ltda and Coreg from Roche Químicos e Farmacêuticos S.A standard reference formulation). A single 25 mg dose of each formulation was administered to healthy volunteers. The study was conducted using an open, randomized, two-period crossover design with a 2-week wash-out interval. Since the 90% CI for C(max) and AUCs ratios were all inside the 80-125% interval proposed by the US Food and Drug Administration Agency, it was concluded that carvedilol formulation elaborated by Laboratórios Biosintética Ltda is bioequivalent to Coreg formulation for both the rate and the extent of absorption.