ABSTRACT: The pharmacokinetic profile of the antibacterial agent florfenicol was studied in plasma after intravenous (i.v.) injection and in plasma, muscle and liver following oral (p.o.) administration to cod Gadusmorhua, held in seawater at 8°C and weighing 100 to 200 g. Following i.v. injection, the plasma drug concentration-time profile showed 2 distinct phases. The plasma distribution half-life (t1/2α) was estimated to be 1.6 h, the elimination half-life (t1/2β) to be 43 h, the total body clearance \\f(Cl _T) to be 0.015 l kg^-1 h^-1 and mean residence time (MRT) to be 74 h. The volume of distribution at steady state, Vd(ss), was calculated to be 1.1 l kg^-1. Following p.o. administration, the bioavailability was estimated to be 91%, the peak plasma concentrations (C max) to be 10.8 µg ml^-1 and the time to peak plasma concentrations (T max) to be 7 h. Corresponding C max and T max values were 13.0 µg g^-1 and 9 h, respectively, in muscle and 12.1 µg g^-1 and 9 h, respectively, in liver. The invitro minimum inhibitory concentration (MIC) values of florfenicol against 3 Vibrioanguillarum strains isolated from diseased cod (A-21, HI-610, HI-618) were 0.5 µg ml^-1 for all 3 strains.