The uptake and distribution of lipopolysaccharide (LPS), isolated from Aeromonas salmonicida, was investigated in Atlantic cod, Gadus morhua L., turbot, Scophthalmus maximus L., and Atlantic halibut, Hippoglossus hippoglossus L. LPS was radiolabelled by bromine oxidation and subsequent sodium borotritide reduction ( 3 H-LPS), and fluorescence-labelled by introducing a fluorescein isothiocyanate derivative (FITC-LPS). After intravenous and intraperitoneal injections in cod,