We measured the pulmonary clearance of [99mTc]DTPA and [99mTc]albumin for 3 h in 10 non-smokers and 10 healthy smokers. Seven of the non-smokers had a monoexponential clearance of [99mTc]DTPA with a mean half-life of 66 +/- 18 min. The other three had a biexponential clearance of [99mTc]DTPA with a fraction of radio-activity clearing rapidly (fF) of 14 +/- 4%. Eight smokers had biexponential clearance of [99mTc]DTPA. The half-life of the fast and slow clearance components was 12 +/- 5 and 62 +/- 11 min respectively. The fF was 56 +/- 25%. Two of the smokers showed a monoexponential clearance of [99mTc]DTPA with a half-life of 72 and 55 min. All non-smokers had monoexponential clearance curves for [99mTc]albumin, compared with seven smokers. The half-life was 279 +/- 43 min in non-smokers and 236 +/- 64 min in smokers. The difference in half-life was not significant. In three smokers, the clearance curves of [99mTc]albumin were significantly better described by a bi-exponential equation. The fF was 22 +/- 9%. The effects of smoking on the clearance of [99mTc] albumin appear to be qualitatively similar to those on the clearance of [99mTc]DTPA. Clearance of [99mTc]albumin seems less sensitive to the effects of smoking than clearance of [99mTc]DTPA.