Benzo[a]pyrene, a lipophilic promutagen, reached maximal concentrations in the thoracic duct lymphatic circulation within 2 h after gastric instillation. Benzo[a]pyrene in lymph obtained by thoracic duct cannulation decreased to approximately control levels within 4 h after treatment. When lymph was not allowed to enter the blood vascular circulation, serum levels of benzofajpyrene increased very slowly, suggesting minimal mesenteric blood vascular absorption of the lipophilic hydrocarbon. Benzo[a]pyrene partitions into lymph Iipoproteins as a function of the lipoprotein concentration. Data suggest that low‐density lipoproteins may take up benzofajpyrene more efficiently than do very low‐density or high‐density lipoproteins, and that lymph components other than lipoproteins do not take up and transport benzofajpyrene. We propose that lipophilic xenobiotic compounds interact with cells of the immune system via lymphatic lipoprotein transport of potentially mutagenic, carcinogenic, or immuno‐suppressive agents.