Ligamenta flava of 100 patients (n = 107 tissue blocks) were examined for the presence of amyloid by means of polarization microscopy after staining with Congo red. Ninety-three ligamenta flava were resected due to operation of herniated discs while 14 ligamenta flava were obtained after surgical treatment of lumbar spinal stenosis. Amyloid of various amounts (score I-III) and 4 morphologically different appearances were detected in the ligamenta flava of 12 patients. In 6 patients small amyloid deposits were seen along elastic fibres (pattern 1) and/or minute, comma-like deposits in certain areas (pattern 2). In 5 other patients amyloid deposits in form of large lumps were present (pattern 3) intermingled with deposits of pattern 1 and/or 2. Only 1 patient could be detected with amyloid deposits partly associated with blood vessels (pattern 4). The amyloid-containing tissue samples (n = 13) were immunohistochemically analyzed using anti-AA-, anti-A lambda-, anti-A kappa-, anti-ATTR- and anti-A beta 2m-antibodies which are able to identify the major known amyloid classes of tissue sections. Tissues with pattern 1 and 2 amyloid deposits did not react above background with any of the antibodies. In contrast, the 5 patients with pattern 3 amyloid stained strongly with anti-ATTR but not with the other antisera. In this group, therefore, senile systemic amyloid (sporadic ATTR) was also identified which had not been detected at this site before. Consistent with this finding is the advanced age of these patients which was seen to be significantly higher than the average age of the entire group of patients examined.