Quasi-reversible electron transfer kinetics are reported for sperm whale myoglobin reacting at tin-doped indium oxide electrodes. This reaction was studied by three different electrochemical methods; cyclic voltammetry (CV), single potential step chronoabsorptometry (SPS/CA) and derivative cyclic voltabsorptometry (DCVA). Kinetic parameters were determined from experiments which followed the purification of the protein, the pretreatment of the electrode surface and the removal of dioxygen from the sample solution. A formal heterogeneous electron transfer rate constant, k 0'. of 2.6 (±0.5) × 10 −5 cm s −1 and a transfer coefficient, α, of 0.48 (±0.05) were obtained using SPS/CA. These results are shown to correlate well with those obtained using a second spectroelectrochemical method, DCVA. Anodic and cathodic responses for the heterogeneous electron transfer of myoglobin can be observed using cyclic voltammetry, but these responses are not as reproducible as those that are obtained using the optical methods described here. The advantages of these optical methods over those of cyclic voltammetry are clear from this study.