Iodophendylate (Pantopaque®) was injected into the spinal subarachnoid space of 56 rats, and a histological examination of the spinal cord, nerve roots and meninges was performed after 1, 4, 8, 16, 30, 60 and 120 days. Bacteriological and roentgenological controls were made. Histological alterations, which in the subgroups seemed very similar, were found in all rats. A moderate unspecific inflammation of the meninges, resulting in a state of fibrous scarring after 120 days, was seen. The meningeal reaction was a little enhanced after injection of blood and iodophendylate, but after 120 days any quantitative differentiation between the two groups could not be made. The endoneurium of the nerve roots displayed a fibrosis parallel to the changes in the meninges. Within the first month, an increasing loss of neurones in the spinal cord was observed. By reducing the injected amount of contrast media the injuring effect on the grey matter was avoided. Ninety rats were myelographied with methiodal (Conturex®) in a suboccipital position. Fifty-five died after a few minutes. The remaining rats all showed a slight, generalized perivascular extravasation of erythrocytes and an acute vacuolization and extreme swelling of the neurones in the grey matter. After 8 days, the number of nerve cells had decreased and any further alterations of the neurones were not noticed. The changes in the meninges were slight and did not differ from those of the rats injected with physiological saline.