A physiological model was developed to estimate fish body toxicant load based on information regarding the chemical exposure regime, fish body weight, lipid content and oxygen uptake. The general model was tested in which an oxygen database (OXYREF) was used to predict fish toxicant body burden. Based on the quantitative analysis, it was shown that the model was reliable and accurate in estimating fish body burden of a number of non-metabolized aquatic toxicants. This modified model possesses some functional reality which enables more realistic predictions, making it useful in the practice of aquatic environmental risk assessment.