Using monodisperse aerosols radiolabeled with (99m)Tc, the authors studied the effectiveness of cough and rapid inhalations for clearing mucus in ten asymptomatic smokers. On three separate study days, each subject breathed 5 micrometers (MMAD) (99m)Tc-iron oxide particles under controlled breathing conditions. While seated in front of a gamma camera, retention (R) of lung activity (measured as a percent of initial activity) was measured over the initial 2 h and again at 24 h following particle inhalation. On the control day the subject sat quietly in front of the camera, while on the cough day each subject performed 60 controlled coughs during the first hour of retention measurements, and on the rapid inhalation study day each subject performed 90 rapid inhalations during the first hour of retention measurements. Because breathing patterns were controlled during particle inhalation, initial lung deposition patterns were matched on control, cough, and rapid inhalation study days. By paired analysis, retentions at both 1 and 2 h R(sub 1) and R(sub 2) for the cough and rapid inhalation measurements were not significantly different from control. Retention at 24 h (R(sub 24)) was not significantly different between cough, rapid inhalation, and control measurements (mean cough R(sub 24)=15 percent, mean rapid inhalation R(sub 24)=14 percent, mean control R(sub 24)=17 percent).