Sixty rats were grown in the presence of 10 (n= 30) and 100 (n= 30)µg kg^–1 body mass of clenbuterol for a period of 10 d. An immunoextraction step coupled with a competitive enzyme immunoassay allowed the quantification of clenbuterol in hair upon 20 (10 µg kg^–1) and 30 d (100 µg kg^–1) after the last dose. This accumulation in hair contrasts with the rapid clearance in tissues. The nature of the immunoreactive material was confirmed by mass spectrometry.