The clinical efficacy of vectrine (erdosteine) was evaluated in the treatment of chronic bronchitis patients with hypersecretion during a controlled clinical trial having included 170 patients. For inclusion, the bronchitis patients had to be in a stable status (no exacerbation since at least three months). The patients received, in double-blind protocol, vectrine, one capsule b.i.d. or placebo, one similar capsule b.i.d. during a period treatment of 21 days. The results of the main evaluation criteria, the global index of efficacy (frequency of the cough + severity of the cough + difficulty in breathing + dyspnea) but also on the intensity and frequency of the cough were statistically significant in favor of vectrine. The safety of the treatment was excellent.