Abstract 1. 1. The results of a clinical study to determine the importance of thorough cleansing of the root canal are reported. 2. 2. Although I do not wish to leave the impression that medication of the root canal is unimportant, for I do use medicaments (including antibiotics) where indicated, no medication other than irrigating solutions was used in this study. 3. 3. The findings indicate that the culture, although important, is not the determining factor for success or failure in therapy. 4. 4. Thorough chemomechanical cleansing of the canal is one of the most important phases of root canal therapy.