A diagnostic protocol for patients with suspected instability and irritative state of a "lumbar motion segment" following lumbar disc surgery is presented and the results of internal fixation are analyzed. In this group of patients the clinical picture and physical signs may be quite distinct and suggestive of instability and irritation of a "lumbar motion segment", however, in isolation, they do not allow to decide upon surgery. Radiological studies favour a decision for surgery only in cases with an obvious instability of a "motion segment". Anaesthethizing the articular nerves permits localization of the irritable segment and non-surgical therapeutic decisions (thermocoagulation) can only be taken in cases of an isolated facet-syndrome when instability has been ruled out. The trial plaster jacket holds the most important position with respect to the indication for internal fixation as demonstrated by the conformity of the results of the plaster jacket and the results of surgery. After internal stabilization excellent, good, satisfactory and moderate results were obtained in 20, 3, 1 and 1 patients, respectively.