This study was undertaken to determine the bioconcentration‐elimination process of fenitrothion in the liver of the european eel(Anguilla anguilla).The animals were exposed to two sublethal fenitrothion concentrations corresponding to 1/5 and 1/10 of LC50 96‐h in a flow‐through test system. Uptake kinetics were determined from liver burdens measured at 2, 8, 24, 48, 56, 72 and 96 hours exposure. After pesticide exposure, animals were transferred to clean water for 72 hours. Fenitrothion elimination was determined after 12, 24, 48 and 72 hours of recovery period. The insecticide showed a high bioconcentration tendency. Steady‐state was reached after 48 hours exposure when the animals where exposed to the lowest concentration. This was followed with a rapid elimination process when the animals were transferred to clean water. Animals exposed to 0.04 ppm showed an early accumulation of the toxicant into the liver, and a steady‐state was reached after 8 hours. The elimination rate constant K2of 0.0096 h‐1and 0.06 h‐1were estimated from the data. The biotransformation rate of fenitrothion in the European eel were low as indicated by a relatively short half‐life (11.55 h) of the insecticide. An increase in the Hepatosomatic Index was observed after 96 hours of exposure, but no significant differences were found between control and exposed animals.