It has been reported that the inhalation of pertechnegas (TGO3) generated under an atmosphere of 3% oxygen (O2) in argon (Ar) instead of 100% Ar without O2 in the technegas generator, offers a simple but accurate quantification of clearance from the lungs, permitting it to be used in place of 99Tcm-diethylenetriamine pentaacetic acid (DTPA). The disappearance from the lungs of inhaled TGO3 was so similar to that of inhaled pertechnetate aerosol (TcO4) in this study, that there was neither a statistically significant difference in the clearance half-time (t1/2), nor a difference in the lung images between them. Neither TGO3 nor TcO4 inhalation could distinguish smokers from non-smokers using t1/2. When inhaled, TGO3 appears to behave in a similar manner to TcO4 in the lungs and hence cannot be used in place of 99Tcm-DTPA in clinical practice.