Three voltammetric enzyme-linked immunoassays based on new systems of o-, m- and p-aminophenol-H2O2-horseradish peroxidase (HRP) have been developed and used for the detection of α-fetoprotein (α FP) in human serum. HRP or labelled HRP catalyzes the oxidation reactions of o-, m- and p-aminophenol with H2O2, the products of which produce three sensitive voltammetric peaks at potentials of −0.87 V, −0.46 V and −0.45 V (vs. SCE) in Britton-Robinson (BR) buffer solution, respectively. By using these voltammetric peaks, the detection limits of α FP are 1.25 ng/mL, 0.5 ng/mL and 0.2 ng/mL, respectively, and the linear ranges 1.25-400 ng/mL, 0.5-400 ng/mL and 0.2-400 ng/mL, respectively. The detection limits of α FP with these methods are lower than that with the enzyme-linked immunosorbent spectrophotometric assay (ELISA).