Levodropropizine is a recently developed, peripherally active antitussive agent which is widely used in clinical practice. In order to obtain further information on the spectrum of activity of this compound in experimental clinical models, a double-blind controlled study was carried out to evaluate the potential effect of the drug against cough and bronchoconstriction induced by inhalation of an ultrasonically nebulized solution of distilled water in patients with obstructive lung disease. Twenty patients were randomly divided into two groups, which received levodropropizine (60 mg t.i.d.) or placebo respectively for 7 consecutive days. Parameters evaluated at baseline and on the last day of treatment included (i) results of respiratory function tests (FEV1, IVC, FVC, TIFF, PEF, MEF75, MEF50, MEF25) performed before the stimulation test with nebulized water; (ii) total number of coughs during a 2-hour period after the stimulation test; (iii) bronchial responsiveness, quantified by calculating the volume of nebulized water required to induce a 20% reduction of FEV1 below the basal level. At pretreatment, the tussive response was very similar in the two groups. A significant decrease in number of coughs (from 34.4 +/- 8.4 at baseline to 15.6 +/- 4.9 post-treatment, p less than 0.01) was observed after administration of levodropropizine, whereas placebo treatment produced no significant effect (number of coughs: 29.6 +/- 4.9 at baseline vs 24.8 +/- 9.6 post-treatment, N.S.). Bronchial responsiveness decreased significantly (compared to baseline) in both treatment groups, without any significant difference between drug and placebo. Respiratory function tests were not significantly affected by either treatment.(ABSTRACT TRUNCATED AT 250 WORDS)