1. Myelograms have been performed in 253 cases of low-back pain with or without sciatica; 206 patients operated upon and the spinal canal was explored.

2. One hundred and thirty-seven positive and twelve negative myelograms were confirmed at operation.

3. Minor discrepancies were noted in seventeen cases or 8.3 per cent., and major discrepancies in forty cases or 19.4 per cent.

4. In 230 cases, 3.3 cubic centimeters of pantopaque was used with ten reactions. In twenty-three cases, larger amounts (6.6 to 17 cubic centimeters) were used with six reactions or 26 per cent. Use of more than 3.3 cubic centimeters was found to be of doubtful value and, even though most of the medium can be removed, the technique is not to be recommended because of the higher incidence of reactions.

5. The presence of an intervertebral-disc lesion and its probable location should be determined from the history and physical examination. If operative treatment is decided upon, the patient may or may not be subjected to a preoperative myelogram.

6. Such a myelogram is a valuable aid in diagnosis and may be a decisive factor in borderline cases. In cases in which operation is clearly indicated, a negative myelogram should be ignored.