The effect of preexisting pulmonary disease on the deposition and retention of inhaled relatively insoluble radiolabeled particles was studied. Two dogs were exposed to 500 ppm sulfur dioxide 2 h/day, 5 days/week for 16 weeks and two dogs were sham-exposed to filtered air for the same period. Dogs exposed to sulfur dioxide developed chronic bronchitis during this exposure period. After the bronchitis had been established for 10 weeks, all 4 dogs were exposed by inhalation to 1.7 micron aerodynamic diameter 134Cs-labeled fused aluminosilicate particles (FAP) and the exposures to SO2 were discontinued. The bronchitis resolved within 4 weeks after SO2 was discontinued. Dogs were periodically whole-body counted and excreta were periodically collected and counted over a 385-day period following the 134Cs exposure. Deposition of the [134Cs]FAP in the pulmonary region averaged 42% for control dogs and 16% for dogs exposed to SO2; deposition in extrapulmonary regions of the respiratory tract averaged 58% for control dogs and 84% for dogs exposed to SO2. Although deposition patterns were different, early and long-term clearance pathways and rates were the same for all dogs, as indicated by analysis of whole body, excreta, and tissues for their burdens of 134Cs.