A double-blind study has been carried out in adult patients suffering from acute and chronic bronchitis, and acute exacerbation of chronic hypersecretory bronchitis, excluding the bronchorreic forms, in order to evaluate the mucolytic activity of orally given domiodol and sobrerol. Treatment with both drugs resulted in an improvement in the subjective measures of ease of expectoration, severity of coughing and sputum consistency; however, there was no improvement in respiratory functions. Moreover, domiodol resulted in a significant increase in sputum volumes, since the very first days of treatment.