One thousand myelographies (370 cervical, 77 thoracic and 553 lumbar examinations) with iohexol (Omnipaque) were performed in 922 patients. No convulsions were seen. Transient hallucinations were reported in one patient. Headache occurred in 38%. The highest frequency of headache (52%) was reported following cervical myelography with lumbar puncture technique, placing the patient horizontally after the examination. The lowest frequency (20%) occurred following cervical myelography with the C1-C2 puncture technique, placing the patient in bed with the head end elevated 20 degrees. Lumbar myelography was performed on an out-patient basis in 243 patients. The frequency of headache was slightly higher (49%) in this group than in the other lumbar myelography patients (34-44%), but no serious complications were seen.