Regional clearance of submicrometric aerosol during 5 days was studied in control hamsters and in those with diffuse interstitial pulmonary fibrosis. Fibrosis was induced by treatment with bleomycin (1.6 U/kg) and oxygen (70% for 72 h) 80 days earlier. Diseased and control animals were exposed for 30 min to an insoluble colloidal 198Au aerosol (AMAD, 0.62 micron; sigma g, 1.35). Five diseased and 6 control animals were killed immediately (Day 0); 6 diseased and 6 control animals were killed 5 days later (Day 5). All lungs were excised, dried at TLC, sliced into 1-mm sections, and dissected into pieces. When compared with deposition in Day 0 control lungs, 26.3% of the particles had been cleared 5 days after exposure from the control lungs. Diseased animals cleared 44.6% of the particles (p less than 0.05, compared with Day 0 diseased animals). Examination of regional clearance on the basis of lobar differences, apex to base levels, and presence of airways also reflected increased clearance in the fibrotic animals. The parenchymal distribution of particle retention at Day 0 was less uniform in the fibrotic animals than in the control animals and was not significantly altered after 5 days of clearance in either group. Particle clearance may be greater in diseased lungs because of accelerated alveolar-bronchiolar transport of particles or particle-containing macrophages.