In a double-blind, randomized, controlled trial using parallel groups, we evaluated the effects of two dose levels of ambroxol (60 and 120 mg daily) versus placebo by means of pulmonary function tests, patients' diary cards, interviews on current airway symptoms and subjective drug effects in 92 subjects with simple hypersecretory chronic bronchitis. The treatment period was 2 weeks. Subjects in the 120-mg group compared to the placebo group reported improvement in respiratory symptoms (p less than 0.05), particularly in phlegm loosening (p less than 0.05) and tended to prefer the treatment period when compared to placebo (p = 0.056). Lung function values and diary cards did not indicate significant changes.