A prospective MRI study was carried out to assess the secondary changes in patients with stenosis and/or herniated disc of the lumbar spinal canal. The study covered 100 patients who had low back and leg pain due to such processes. Of these, 60 patients (group A) had a monoradicular pain pattern, average duration 2 months, due to a herniated lumbar disc. The remaining 40 patients (group B) had acute exacerbation of their chronic low back and leg pain, due to stenosis and herniated disc. As a control group, 5 asymptomatic volunteers with neither stenosis nor herniated disc on MRI were examined. All the patients and volunteers were examined by MRI with several sequences: partial saturation recovery with phase contrast PS (500/10), spin echo SE (500/20), short TI inversion recovery STIR (1900/135/30) and, for the dynamic study, field-gradient echo sequences FAST (50/15): 10 frames in 200 s. In all participants, Gd-DTPA was administered intravenously. In 8 of the patients of group B capillarisation in the protruded nucleus tissue was demonstrated on the PS sequence after Gd-DTPA administration. This tissue also showed decreased signal intensity on the STIR sequence. The capillarisation extended into the centre of the disc. Venous stasis could be verified in all of the 100 patients. An oedema could be verified in all patients of group A; in 20%, its size exceeded that of the herniated disc. In group B, an oedema was seen in only 12 patients. In the control group, no haemodynamic changes were seen. Using MRI, it is possible to define the border between herniated disc tissue and perifocal oedema.(ABSTRACT TRUNCATED AT 250 WORDS)