A competitive enzyme immunoassay (EIA) for the detection and quantitation of zeranol has been developed. The assay involves the use of excess second antibody adsorbed onto the walls of a microtitration plate well. Enzyme‐labelled zeranol, prepared by theN‐succinimidyl ester method, and standard or samples are added to the wells followed by zeranol‐specific monoclonal antibody. The working range of the EIA is between 10 and 800 pg/well with a limit of detection of 10 pg/well (CV ≤ 10%). Comparison of radioimmunoassy with the EIA gave a correlation coefficient of 0.99. This EIA offers an alternative to the well‐documented radioimmunoassay with regard to sensitivity, specificity and precision.