Electrochemical reduction of the dacarbazine-Cu2+ complex was investigated using cyclic voltammetry and square wave voltammetry at a hanging mercury drop electrode. The reduction of the dacarbazine-Cu2+ complex is irreversible. A reduction mechanism is proposed comprising a one-electron reduction of the Cu2+ directly within the complex. The sharp peak of the adsorbed dacarbazine-Cu2+ complex associated with an effective interfacial accumulation facilitates the determination of the anticancer drug dacarbazine in pharmaceutical formulations and biological fluids. Detection limits for dacarbazine of 6.121010 M, 1.571010 M and 1.97109 M were achieved for the determination of the drug in vial, human urine and serum, respectively.