Résumé : A radioimmunoassay for clenbuterol detection in cattle has been validated and used to monitor treated cattle. The tracer used was 4-amino-3,5-dichloro-α (tert-butylaminomethyl) benzyl alcohol (benzyl-3H) (clenbuterol) prepared by catalytic tritiation with tritium gas of 4-amino-3,5-dibromo-α-(tert-butylamino)-acetophenone, followed by chlorination at positions 3 and 5 in the aromatic ring. The rabbit antiserum was raised against a diazotized clenbuterol/human serum albumin conjugate. The assay described was sensitive (7.8 pg/tube) and reproducible. The intra- and inter-assay variability, which was assessed by measuring known quantities of clenbuterol in plasma, urine and faeces, was satisfactory for RIA. When this assay was used to monitor treated cattle the concentrations of clenbuterol in plasma, urine and faeces were directly related to the administered dose. The absorption and elimination of clenbuterol in cattle was rapid. Data obtained were consistent with results obtained in other species where a rapid clearance rate was also demonstrated. © 1991 Taylor & Francis Group, LLC.