The applicability of sonography in the control of preoperative radiotherapy of neck lymph nodes in patients with malignancies in the region of the head and the neck was established in a prospective study. Lymph nodes with positive reactions showed a simultaneous reduction in size and structure. Postoperative histology showed no malignancy in these lymph nodes. All metastases were found in lymph nodes without sonographic changes under irradiation. In establishing the surgical procedure, clinical criteria should be considered primarily, and these should be supplemented and completed by the sonographic investigation.