A biting behavior in the Moroccan pond tortoise (Clemmys caspica leprosa) after apomorphine administration is described. The biting behavior was antagonized by the specific anti-dopaminergic drug haloperidol (10 mg/kg) and trifluperazine (15 mg/kg). The behavior was compared to similar behaviors in birds and mammals. The dopamine metabolites, homovanillic acid and 3,4-dihydroxyphenylacetic acid, were measured by a gas chromatographic method in the tortoise brain. From the effects on behavior and the changes in the level of these metabolites upon drug administration it was concluded that the dopamine system in the tortoise is qualitatively similar to that in birds and mammals but less sensitive to blockade.