The electrooxidative behavior and determination of Verapamil HCl, one of the class IV anti-arrhythmic agent, on a glassy carbon disc electrode were investigated for the first time by using cyclic, differential pulse (DPV), and Osteryoung square wave voltammetry (OSWV). Verapamil showed an irreversible oxidation behavior at all pH values and buffers studied. From the electrochemical response, the main oxidation step was found to be related to the methoxy group on the phenyl ring. DPV and OSWV were used to generate peak current versus concentration curves for verapamil. A linear response was obtained in the range comprised between 8 x 10(-7) and 1 x 10(-4) M for both techniques with detection limit of 1.61 x 10(-7) M for DPV and 1.33 x 10(-7) M for OSWV. The repeatability and reproducibility of the methods for all investigated media (such as supporting electrolyte and serum samples) were determined. Precision and accuracy were also checked in all media. The methods were proposed for the determination of verapamil in dosage forms adopting both DPV and OSWV modes. The methods were extended to the in vitro determination of verapamil in spiked serum samples. No electroactive interferences from the endogenous substances were found in human plasma.