The voltammetric behaviour of resazurin in the presence of Cd2+ and Zn2+ ions at a hanging mercury drop electrode (HMDE) was investigated by using square wave voltammetry (SWV), cyclic voltammetry (CV) and adsorptive square wave voltammetry (AdsSWV). The interaction of resazurin with Cd2+ and Zn2+ starts above pH 4 and seems to be completed at pH 5.2 with Cd2+ ions and at pH 7.5 with Zn2+ ions. A new peak appears at -0.93 V in the presence of Cd2+ and at -1.07 V in the presence of Zn2+. These peaks may be attributed to M2+-resazurin complexes and the logarithm of their stability constant was determined where log beta(1:1) = 4.22 for Cd2+-resazurin and log beta(1:1) = 4.74 for Zn2+-resazurin. Cyclic voltammetry was used to characterize the redox mechanism and to calculate voltammetric data of M2+-resazurin complexes. The amount of adsorbed M2+-resazurin complexes on the mercury drop electrode surface (Gamma) is calculated as 5.48 x 10(-12) mol cm(-2) for Cd2+-resazurin and 1.10 x 10(-11) mol cm(-2) for Zn2+-resazurin. The voltammetric data were compared with the data obtained using spectrophotometric methods and were observed to be in good agreement.