In a series of 100 consecutive patients surgically treated for Zenker's diverticulum (ZD) biopsy specimens were taken at the level of the cricopharyngeal muscle in 62 patients and also at the level of the striated muscle wall of the cervical esophagus in 10 patients. Contractility, pathological enzymo- and immunohistochemical characteristics were studied in comparison with a group of 15 controls. Obvious pathological findings were noted in 95% of the ZD specimens as compared with the control specimens. These pathological changes, although somewhat less pronounced, were also documented in the biopsy specimens taken at the level of the striated cervical muscle wall. The findings were judged important enough to justify a long extramucosal myotomy of the cricopharyngeal muscle and cervical esophagus as an essential step in the treatment of ZD. The treatment of choice in this series was a diverticulopexy and a four to five centimeter long extramucosal myotomy, starting from the cricopharyngeal muscle and extending downwards into the striated muscle wall of the cervical esophagus. Excellent or very good results were obtained in 96% of the patients with respect to diverticulum-related symptoms.