The density of metrizamide injected accidentally into the spinal cord during cervical CT myelography was measured with CT scanning and compared with a series of dilutions of metrizamide scanned with a special phantom. The test suggests that the metrizamide is diluted rapidly in the spinal canal, and in an accidental intraspinal injection of metrizamide, it is not the contrast medium itself but the mechanical effect of the introduction of a volume of fluid that causes the neurological symptoms.