Bioconcentration factor (BCF) is the concentration of a chemical in an organism divided by the concentration in water and it is one of the most important indicators for the fate of chemicals in the environment. Present methods for a preliminary estimation of concentration of hazardous chemicals in biota are based on empirical parameters, like water solubility (WS) and octanol-water partition coefficient (Kow). The accuracy of these methods is very low and experimental determination of empirical parameters can be very costly and time consuming. Thus, a novel, practical and efficient, method for prediction of BCFs of hazardous chemicals has been proposed. Molecular connectivity indices, based on molecular topology (number and type of atoms and chemical bonds), are purely non-empirical data and their calculation is quite simple. Second-order valence molecular connectivity indices were found to correlate extremely well with the BCFs in fish, obtained from the flowing water method, for various halocarbons (hydrocarbons, benzenes, biphenyls and diphenyloxides). Several well known and extensively used pesticides (DDT, DDD, DDE, heptachlor and dieldrin) have been chosen to test the predictive ability of the equation describing parabolic relationship between second-order valence molecular connectivity indices and BCFs.