A double-blind study versus placebo was performed to assess the effect of bamiphylline, a new xanthylic derivative, on tracheobronchial mucus clearance (TBMC) in smokers with simple chronic bronchitis and impaired mucus clearance as compared to normal controls. Twenty patients were enrolled and divided into two randomized groups. The first group was treated with bamiphylline (600 mg b.d.) for 15 days, while the second group received placebo with the same oral dosage regimen. Complete clinical-functional examinations were made before and after the test period to establish the effects of treatment. At the end of the study, only the group treated with bamiphylline showed a net increase in mucus clearance (mean radioaerosol elimination 28 +/- 7% before treatment and 38 +/- 11% after treatment; p < 0.01) and an improvement in the clinical score and pulmonary function parameters, in particular the residual volume (RV = 3.41 +/- 0.75 liters before treatment and 2.7 +/- 0.6 after treatment; p < 0.01) and the forced expiratory volume at 1 s (FEV1 = 2.37 +/- 0.7 liters before treatment and 2.88 +/- 0.5 after treatment; p < 0.05). No side effects or adverse reactions that could be attributed to the study drug were observed.