The kinetics of 1,2,4-trichlorobenzene in guppies (Poecilia reticulata) have been studied in an accumulation and elimination experiment. At a sublethal exposure, uptake and elimination rate constants of 1,2,4-trichlorobenzene were determined, employing a first-order one-compartment model. The constants were found to be 492 ± 234 Lkg−1 d−1 (uptake), and 0.49 ± 0.22 d−1 (elimination) on the basis of wet weight. Exposing guppies to a time-varying lethal concentration of 1,2,4-trichlorobenzene for three weeks, it was found that the model gives a satisfactorily prediction of fish residues at lethal exposures on the basis of toxicokinetic parameters determined at sublethal exposures. During the first days residues were over-estimated. This may be due to a period of immobility before fish are dying. Kinetic parameters may be lower during immobility.