A new structure was found in the spinal ganglia of 6 out of 215 human autopsy cases with various disorders. It was composed of ballooned cells fully packed with fibrillar structures showing the same staining properties as collagen. Ultrastructurally the fibrillar structures were bundles of collagen fibres with a striation of about 70nm periodicity, and they were enclosed by the cell membrane invaginated in a very complex manner into the cytoplasm. This structure, which we named 'pseudo-intracellular collagen tangle', was considered to result from a disturbance in the releasing process of collagen fibre from fibroblasts. The aetiology of the structure is unknown, but it might represent one of regressive or senile changes in human spinal ganglia.