A mathematical model simulating the blood transport and tissue residue distributions of the highly toxic and highly lipid soluble pesticide dieldrin in mammals is presented. This model is a significant improvement over our previously published preliminary model for dieldrin distribution in mammals. The assumptions and working hypotheses of the model are presented and used in generating a set of differential equations based upon mass balance principles. Two simulation cases are examined. The first simply demonstrates the gross features of: 1) Transport limiting conditions; 2) equal transport-equal membrane transfer conditions, and 3) membrane transfer limit conditions. The second studies a single tissue (the blood-brain barrier case) example of the above mentioned conditions. All simulations made were conducted for a hypothetical mature male rate of the average Wistar type eating food ad lib.