Trenbolone is a xenobiotic anabolic compound with androgenic growth promoting activities which is prohibited for use in the EC member states. The following cross-reactivities were demonstrated for this Trenbolone-EIA: 17-ß-trenbolone (100%), 17a-trenbolone (63%), altrenogest (38%), 19-nortestosterone (2%). Endogenous androgens showed less than 0.01 % cross-reactivity. In urine samples, trenbolone can be demonstrated down to a detection limit of 0.5 ng/ml, after a simple extraction method.