A novel homogeneous electrogenerated chemiluminescence immunoassay (ECLIA) for the determination of small hapten was developed. As a model system, digoxin was investigated while luminol served as luminescence label and BSA served as carrier protein. Digoxin was indirectly heavily labeled with luminol throughBSAto form luminol-BSA-digoxin conjugate. The immunocomplex of luminol-BSA-digoxin conjugate with anti-digoxin antibody underwent less ECL reaction than luminol-BSA-digoxin conjugate after immunoreaction took place. Two immunoassay formats, directly homogeneous immunodetection for anti-digoxin antibody and competitive immunoassay for digoxin, were proposed to determine anti-digoxin antibody and digoxin, respectively. The anti-digoxin antibody concentration was determined in the range from 1/50,000 to 1/2000 dilution. The ECL intensity versus digoxin concentration was linear in the range from 5.0×10−10 to 3.0×0−8 gml−1. The detection limit was 2.8×10−10 gml−1. The relative standard derivation for 1.0×10−9 gml−1 was 5.1%. The proposed method has been applied to assay digoxin in human control serum with satisfactory results.