Description: 17beta-testosterone (testosterone) and 17beta-estradiol (estradiol), together with their synthetic analogues, have been banned in the EU as growth promoters for fattening purposes. A simple, reliable method for their detection in animals is therefore required. Levels of testosterone and estradiol in hair and plasma of Wistar rats have been determined, following intramuscular (i.m.) administration of testosterone propionate and estradiol valerate, using commercial ELISA kits. Experiments were performed on prepubertal female rats for the detection of hair testosterone and on prepubertal male rats for the detection of hair estradiol. A significant increase of testosterone in hair was observed 3, 6 and 9 days after the administration of testosterone propionate, with no significant change in plasma content. Estradiol valerate administration also resulted in a significantly increased concentration in hair on the 3rd and 9th days, and in plasma on the 9th day. Thus, detection of testosterone and estradiol in hair after i.m. testosterone propionate and estradiol valerate administration can be achieved using commercial ELISA kits. Up to 0.80 percentage of the administered testosterone and 0.06 percentage of the administered estradiol were present in hair. This method could therefore serve as the basis for establishing a pre-screening tool for detecting abuse of anabolic steroids in farm animals