Papers on deposition pattern analyses of radio-aerosol lung scans are few and not easy to interpret as there is a general lack of technical standardization and the number of patients studied is not large. Moreover these reports have been generally obtained with non-hydrosoluble radioaerosols. In the present study 43 patients underwent conventional pulmonary function testing and lung scanning using small droplet (equal or less than 2 microns) polydisperse 99mTc-DTPA radioaerosol produced with the "Settling Bag System"--Medi 400 (Sorin). The scans were analysed by two methods: a semiquantitative method proposed by Taplin (SQT); an original simpler semiquantitative method (SQM). Correlations of SQT and SQM with FEV1 and MEF75 resulted highly significant (p less than 0,001). SQM proved to be superior to SQT as far as reproducibility is concerned. The following conclusions can be drawn: small particle 99mTc-DTPA aerosol can be easily and cheaply produced by a commercial device; such a radioaerosol is well suited for the evaluation of small and large airways patency, as reflected by MEF75 and FEV1 respectively, with a diagnostic yield comparable to non-hydrosoluble radioaerosols; the original semiquantitative description of the deposition patterns proposed and validated in this study is quite easy to implement and it yields a high correlation with pulmonary function tests; moreover such an approach does not require digital data processing; the sensitivity of 99mTc-DTPA for the diagnosis of bronchial obstruction is very high and superior to routine pulmonary function tests; in addition the ventilation scan allows the topographical localization of the obstructions themselves.