F344 rats were chronically exposed to diesel exhaust at target soot concentrations of 0 (control, C), 0.35 (low, L), 3.5 (medium, M), and 7.0 (high, H) mg/m3. Accumulated lung burdens of diesel soot were measured after 6, 12, 18, and 24 months of exposure. Parallel measurements of particle deposition and clearance were made to provide insight into the mechanisms of particle accumulation in lungs. The fractional deposition of inhaled 67Ga2O3 particles after 6, 12, 18, and 24 months of exposure and of inhaled 134Cs-fused aluminosilicate particles after 24 months were similar for all groups. Progressive increases in lung burdens of soot particles were observed in M and H exposed rats, reaching levels of 11.5 +/- 0.5 and 20.5 +/- 0.8 mg/lung (mean +/- SE), respectively, after 24 months. Rats in the L group had smaller relative increases in lung burden, reaching levels of 0.60 +/- 0.02 mg/lung after 24 months. Tracheal mucociliary clearance measurements, using 99mTc-macroaggregated albumin deposited in the trachea, showed no changes at anytime. There were statistically significant increases in clearance half-times of inhaled radiolabeled particles of 67Ga2O3 as early as 6 months at the H level and 18 months at the M level; no significant changes were seen at the L level. Rats inhaled fused aluminosilicate particles labeled with 134Cs after 24 months of diesel exhaust exposure to measure long-term components of pulmonary clearance. The long-term clearance half-times were 79 +/- 5, 81 +/- 5, 264 +/- 50, and 240 +/- 50 days (mean +/- SE) for the C, L, M, and H groups, respectively. Differences were significant between the C and both the M and H exposure groups (p less than 0.01). Lung burdens of diesel soot were more than expected at the H and M levels and were also associated with impaired particle clearance while smaller responses were observed in both burdens and clearance at the L level.