Currently there are few antibacterial dosage regimens established to be safe and effective for sea turtles. Pharmacokinetic evaluation of antibiotics is an essential step in establishing accurate dosage guidelines for a particular species. Metronidazole is an antibiotic that is effective against anaerobic bacteria and some protozoa. For most anaerobic bacteria, the minimum inhibitory concentration (MIC) for metronidazole ranges from 0.25 to 4.0 µg/ml. The MIC values for some Clostridium species are up to 8 µg/ml, and for protozoal agents of trichomoniasis (MIC of 0.05 µg/ml), amebiasis, and giardiasis the MIC ranges from 1 to 50 µg/ml. The objective of this study was to determine the pharmacokinetic parameters after administration of metronidazole to aid in the establishment of species-specific dose guidelines in green (Chelonia mydas), loggerhead (Caretta caretta), and Kemp's ridley (Lepidochelys kempii) sea turtles. After administering metronidazole at a dose of 20 mg/kg orally and IV, the pharmacokinetics were very similar for these three species of sea turtles (n = 6 for each species). For both oral and IV routes of administration, plasma metronidazole concentrations were maintained above 8 µg/ml for approximately 24 h and above 4 µg/ml for approximately 48 h; however, plasma concentrations of 8 µg/ml were reached within 5 min only for the IV route, versus 8 h for the oral route.