The objective of this study was to evaluate the pharmacokinetic profiles of toltrazuril (TZR), and its major metabolites toltrazuril sulfoxide (TZR x SO) and toltrazuril sulfone (TZR x SO(2)) in rabbits after oral administrations. Rabbits were dosed once with 10 and 20mg/kg TZR via stomach tube with manual restraint. The plasma concentrations of TZR, TZR x SO and TZR x SO(2) were determined by liquid chromatography/mass spectrometry. Plasma concentration-time data after single oral administration were analyzed by a non-compartmental analysis. Plasma peak concentrations of TZR, TZR x SO and TZR x SO(2) were 30.2+/-1.5microg/mL at 20.0+/-6.9h, 8.9+/-1.3microg/mL at 20.0+/-6.9h and 14.7+/-3.9microg/mL at 96.0+/-0.0h after oral administration of TZR with 10mg/kg bw, respectively. The terminal elimination half-lives for TZR, TZR x SO and TZR x SO(2) after oral dose of 10mg/kg were 52.7+/-3.6, 56.1+/-10.7 and 76.7+/-7.5h, respectively. Plasma peak concentrations of TZR, TZR x SO and TZR x SO(2) were 39.4+/-1.2microg/mL at 28.0+/-6.9h, 12.5+/-3.9microg/mL at 20.0+/-6.9h and 24.9+/-8.74microg/mL at 112.0+/-6.9h after oral administration of TZR with 20mg/kg bw, respectively. The terminal elimination half-lives for TZR, TZR x SO and TZR x SO(2) after oral dose of 20mg/kg were 56.7+/-1.9, 68.8+/-12.5 and 82.3+/-12.6h, respectively. In conclusion, TZR was very well-absorbed through the gastrointestinal tract and rapidly metabolized to TZR x SO and TZR x SO(2) in rabbits after oral administration. TZR x SO(2) was actually more slowly eliminated than TZR and TZR x SO.