The electrogenerated chemiluminescence (ECL) behavior of lucigenin on a mesoporous platinum electrode has been studied in neutral aqueous solution (pH 7). The present mesoporous Pt electrode with highly enlarged surface area, with a roughness factor of 301, exhibits much larger electrochemical responses for the oxidation of water and the reduction of molecular oxygen, which leads to much larger lucigenin ECL responses related to the anodic and cathodic electrochemical reactions even in a neutral solution, compared to those at a bare Pt electrode. Based on the capability of superoxide dismutase (SOD) to inhibit lucigenin ECL by scavenging superoxide anions, a highly sensitive ECL bioassay for SOD has been developed with a linear dynamic range of 5.75 x 10(-10) M-3.00 x 10(-6) M and a detection limit of 3.49 x 10(-10) M (S/N = 3), which is much lower than those obtained with other detection methods.