Abstract <p>A highly sensitive square-wave adsorptive anodic stripping voltammetric method is described for the determination of ribavirin in its pharmaceutical formulations and human blood serum, utilizing a carbon paste electrode. The peak current was significantly enhanced due to the strong adsorptive properties of the drug at the electrode surface. The optimal procedural parameters were: frequency of 20 Hz, scan increment of 4 mV, pulse amplitude of 25 mV, and accumulation potential of –0.5 V versus Ag/AgCl/3 M KCl in Britton–Robinson buffer at pH 8.0. The described method was successfully applied for the assay of ribavirin in its pharmaceutical formulation (Ribavirin^® capsules, 200 mg ribavirin), with mean percentage recoveries of (98.3 ± 1.3)%. Furthermore, the method was successfully applied for the assay of ribavirin in spiked human blood serum without the necessity for sample pretreatment or time-consuming extraction prior to analysis. The mean percentage recovery of ribavirin in human blood serum was (98.6 ± 1.1)% (<i>n</i> = 5), with a limit of detection of 1 × 10^–9 M (0.24 ng/mL). Due to this extremely low limit of detection, the proposed method can be applied in pharmacokinetic and pharmacodynamic studies of the drug.</p>