The disposition kinetics of marbofloxacin at a single dose of 2 mg/kg bodyweight were determined in a crossover trial with five clinically healthy loggerhead sea turtles (Caretta caretta) after i.v. and i.m. administration. Marbofloxacin plasma concentrations were determined by high-performance liquid chromatography (LOD/LOQ 0.05 µg/ml). Data were subjected to noncompartmental analysis. The integrated pharmacokinetic/pharmacodynamic variables showed that optimal area under the curve (AUC_{0–24 h}): minimal inhibitory concentration (MIC) (>125) and C_max: MIC (>8) ratios, as reported for concentration-dependent bactericidal antimicrobials (e.g., fluoroquinolones), were achievable with both a once daily i.v. or i.m. dose for microorganisms with MIC ≤ 0.5 µg/ml, while a C_max: MIC > 8 for MIC ≥ 1 µg/ml was achievable only after the i.v. administration. The absence of adverse reactions in the animals after i.v. or i.m. administration of marbofloxacin and the favorable pharmacokinetic/pharmacodynamic properties after a single dose of 2 mg/kg suggest the possibility of its safe and effective clinical use in loggerhead sea turtles.