Enrofloxacin (Baytril®) is a recently released chemotherapeutic agent of the quinolone carboxylic acid group which is structurally related to nalidixic acid and norfloxacin and is licensed for veterinary use only. Its unique mechanism of action, high bioavailability via oral route, and excellent body tissue/ fluid compartment concentrations attained make enrofloxacin particularly promising in use with marine mammals. Although there have been infrequent reports of neurologic, hematologic, gastrointestinal, and cartilaginous toxicities associated with enrofloxacin, the drug's use in a variety of domestic and exotic animal species has been very well tolerated. All information to date on enrofloxacin suggests that the drug holds great promise as a potent chemotherapeutic agent in a variety of bacterial diseases. Ascertaining proper dosage guidelines for enrofloxacin in marine mammals, and cetaceans in particular, would prove advantageous to veterinarians involved in this specialized area of practice. Eight adult Atlantic bottlenose dolphins Tursiops truncatus (6 male, 2 female) were selected to participate in a single-dose study of the pharmacokinetics of orally administered enrofloxacin dosed at 5mg/kg body weight. Blood samples were taken from all animals at 0, 2, 4, 8, 12, and 24 hours following administration of the drug. Serum drug concentration levels were determined via bioassay, which measures the total biological activity of a drug by comparison with a reference standard. Based upon the observed data, the average half-life of enrofloxacin in the study animals was approximately 7 hours with a range from 3.4 to 11.0 hours. Absorption was somewhat variable with the point of maximal serum concentration ranging from 2 to 8 hours following a single oral dose of 5mg/kg. The variation in absorption can most likely be attributed to individual differences in the storage and digestion of the fish ration containing the drug dose within the compartmentalized cetacean stomach.