A non-competitive immunoassay was performed by sodium dodecyl sulfate-capillary gel electrophoresis with UV detection using bovine serum albumin (BSA) and monoclonal anti-BSA. BSA, anti-BSA and their immunocomplexes were well resolved under non-denaturing conditions. A linear calibration curve was obtained and can be used for the quantification of anti-BSA. The limit of detection of anti-BSA was 0.1 microM under the present conditions. Compared with capillary zone electrophoresis, we believed that this method has the potential to be used as a more general format for performing capillary electrophoresis-based immunoassay of medium- and large-sized analytes.