A cathodically pretreated boron-doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry. Linear calibration curves (r ¼ 0.999) were obtained from 1.9 Â 10 À5 to 2.1 Â 10 À4 mol L À1 for AA and from 9.7 Â 10 À6 to 1.1 Â 10 À4 mol L À1 for CAF, with detection limits of 19 mmol L À1 and 7.0 mmol L
À1, respectively. This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations, with results equal to those obtained using a HPLC reference method.