Ambroxol, a metabolite of bromhexine, was investigated in a double-blind, controlled trial using parallel groups. We studied the effects of 60 mg and 120 mg daily versus placebo in subjects with simple chronic bronchitis. Possible therapeutic effects were evaluated by means of interviews on subjective drug effects and current respiratory symptomatology, patient diary cards, and lung function tests. Ninety-seven subjects entered the study and 92 completed satisfactorily. Comparison with the placebo group at the end of the study showed that significantly more subjects in the 120 mg ambroxol group reported improvement in respiratory symptoms, principally improved expectoration. Subjects in the 120 mg group tended to prefer the treatment period when compared to placebo but the diary cards did not indicate significant changes. Lung function values were mainly normal and did not change during treatment. We conclude that the drug had a symptomatic effect and that further studies in more severely affected patients would be worthwhile.