A simple partition model was developed to evaluate the bioaccumulation of chlorinated hydrocarbon pesticides (dieldrin and heptachlor) in the soil-pasture-grazing animal system. Biomagnification factors (BFL) calculated on a lipid basis ranged from 0.115 to 0.175, but could not be directly compared with other values from the literature because of different methods of calculation. The partition model predicted values of somewhat less than unity, indicating that it does not fully account for pesticide pathways and mechanisms. However, the lack of variation of these values from two compounds indicates a lack of dependence on the octanol/water coefficient which is in accord with the model. The results suggest partitioning between food in the stomach and body tissues is a major bioaccumulation process but other major processes are also involved.