An experimental method for testing contrast media for myelography was developed and used to compare three watersoluble contrast media, iocarmate meglumine, iothalamate meglumine and metrizamide after suboccipital myelography in 120 rabbits. A further 71 rabbits served as controls. Iocarmate and iothalamate caused vigorous convulsions; metrizamide did not. Examination of the CSF revealed an acute pleocytosis after installation of the contrast media and after cisternal puncture with injection of hypertonic saline. Histological examination of the spinal cord, nerve roots and meninges revealed pathological changes in 1 or 32 unoperatec controls (3%). Leucocyte infiltrations were found in the meninges, nerve roots and spinal cord of about 20% of the animals after myelography, after cisternal puncture without injection or with injection of hypertonic saline. There were no significant quantitative differences between the experimental groups. Degenerative changes were seen only after myelography. No meningeal fibrosis was demonstrated. An abnormal leucocyte count in the primary CSF influenced the incidence of histological changes, indicating that only rabbits with CSF cell counts within normal limits should be used in future experiments.