In this study, the pharmacokinetic profile of enrofloxacin (EF) and its major metabolite, ciprofloxacin (CF), were investigated in brown trout (Salmo trutta fario) (n = 150) after intravenous (i.v.) and oral (p.o.) administrations of a single dose of 10 mg kg- 1 body weight (b.w.) at 10 °C. The plasma concentrations of the drugs were determined by high-performance liquid chromatography (HPLC-UV) from 0.08 to 120 h. Pharmacokinetic parameters were described by the two-compartment open model for intravenous and oral administrations, respectively. After intravenous administration, the elimination half-life (t1/2β), apparent volume of distribution at steady-state (Vss) and total body clearance (Cltot) of enrofloxacin were 19.14 ± 1.51 h, 3.40 ± 0.18 L kg- 1 and 0.14 ± 0.01 L kg h- 1, respectively. After oral administration, the maximum plasma concentration (Cmax), time of maximum concentration (tmax) and bioavailability (F%) were 2.30 ± 0.08 μg mL- 1, 8 h and 78 ± 4%, respectively. Ciprofloxacin was not detected in the present study. The elimination half-life for enrofloxacin following oral administration was longer than values calculated for other animals. After oral administration, the mean plasma concentration was well above the minimum inhibitory concentrations (MICs)-that is, > 0.5 μg mL- 1 at 36 h-for most gram-negative fish pathogens. It is possible and practical to obtain therapeutic blood concentrations of enrofloxacin in brown trout (S. trutta fario) using oral administration of 10 mg kg- 1 body weight; therefore, it may be effective in the therapy for brown trout diseases. © 2009 Elsevier B.V. All rights reserved.