beta -agonists are compounds having a stimulatory effect on beta -adrenergic receptors and are used in human and veterinary medicine as bronchodilatory agents. The group includes drugs such as clenbuterol, carbuterol, salbutamol, methylclenbuterol, brombuterol, terbutaline, mabuterol, pirbuterol and mapenterol. The metabolism of beta -agonists is dependent on the chemical properties of each drug, with excretion reported in bile, urine, faeces and milk. Accumulation of beta -agonists has been reported in tissues including liver, kidney and pigmented tissue e.g. retina.