Plasma concentrations and pharmacokinetics of enrofloxacin were determined in 12 loggerhead sea turtles (Caretta caretta) after oral administration. Six turtles in group 1 and group 2 received enrofloxacin at 10 mg/kg and 20 mg/kg of body weight, respectively. Blood was collected from the cervical sinus before administration and at timed intervals up to 168 hr following administration. Plasma concentrations of enrofloxacin were determined using a microbiologic assay. The mean peak plasma concentration (C_max) was 4.07 μg/ml and 21.30 μg/ml for groups 1 and 2, respectively. Plasma levels were detectable at 168 hr postadministration, with mean values of 0.380 μg/ml for group 1 and 2.769 μg/ml for group 2. The mean elimination half-life for enrofloxacin was 37.80 hr for group 1 and 54.42 hr for group 2. These findings indicated that enrofloxacin is absorbed following oral administration in loggerhead sea turtles, and blood levels are maintained up to 168 hr following administration.