Mice were exposed to diesel exhaust for 9 months prior to evaluation for benzo(a)pyrene disposition. On the last day of exposure the mice were instilled intratracheally with tritiated-benzo(a)pyrene ([3H]BP). The mice were sacrificed at intervals of 2, 24, and 168 hours. Disappearance of radioactivity from lungs and liver was rapid and essentially linear with time. In lungs, liver, and testes; [3H]BP metabolites were found mainly as conjugates, a form readily excretable. Clearance of the hydrocarbon from liver and testes in exposed mice was not markedly different from that in nonexposed mice. However, mice exposed to diesel exhaust had delayed [3H]BP clearance from lungs, possibly due to [3H]BP adsorption to diesel smoke particles.