Three captive loggerhead sea turtles, Caretta caretta, were used in four trials, one i.v. and three i.m., to determine the pharmacokinetic properties of a single dose of ticarcillin. For the i.v. study, each turtle received a single 50 mg/kg dose and blood samples were collected at 0, 0.5, 1, 2, 4, 6, 8, and 12 hr and at 1, 1.5, 2, 2.5, 3, 4, 6, 8, 10, and 14 days after administration. For the i.m. study, each turtle received one of three dosages (25, 50, or 100 mg/kg) in a randomized complete block design and blood samples were collected at the same time intervals. Each trial was separated by a minimum of 28 days to allow for complete drug clearance. Drug concentration in plasma was determined by a validated liquid chromatography–mass spectrometry assay. For the i.v. study, the elimination half-life was 5.0 hr. The apparent volume of distribution and plasma clearance were 0.17 L/kg and 0.0218 L/hr/kg, respectively. For the i.m. study, mean time to maximum plasma concentrations ranged from 1.7 (±0.58) hr in the 50 mg/kg group to 3.7 (±2.5) hr in the 100 mg/kg group. Mean bioavailability ranged from 45% (±15%) in the 50 mg/kg group to 58% (±12%) in the 100 mg/kg group, and the mean residence time ranged from 7.5 (±2.6) hr in the 25 mg/kg group to 16 (±6.8) hr in the 100 mg/kg group. Two turtles had slight alanine aminotransferase elevations that were not clinically apparent at two different dosages, but otherwise, blood chemistries were unaffected. Possible i.m. dosage regimens for loggerhead sea turtles are 50 mg/kg q24 hr or 100 mg/kg q48 hr. Liver enzymes should be monitored during treatment.