This study reports the uptake and elimination kinetics, the bioconcentration, and the acute toxicity of a series of chlorinated benzenes and biphenyls in a submerged aquatic macrophyte (Myriophyllum spicatum) and in a fish (Poecilia reticulata) species. The objective of this study is to investigate the relationship between the acute lethality in fish and in aquatic plants. The study shows linear relationships between the plant-water and fish-water bioconcentration factors and the 1-octanol-water partition coefficient, indicating that plant-water and fish-water exchange are largely controlled by the chemical's tendency to partition between the lipids of the plants or fish and the water. The toxicokinetics in both the plants and the fish involve “passive” transport phenomena, which can be described by a lipid-water kinetic model. Toxicity data demonstrate that the acute lethality of chlorobenzene and chlorobiphenyl congeners in fish is associated with an internal concentration in the fish of approximately 6330 μmol/L. Based on the similarity of the lethal internal concentration among the chlorobenzene congeners and between various aquatic organisms, it is hypothesized that the acute lethal toxicity of chlorobenzenes in plants and fish are similar, which would provide a basis for the extrapolation of toxicity data between fish and aquatic plants.