We have previously described our experiences with pantopaque, including the spinal fluid reaction and the comparative value of the medium in contrast myelography (2). Preliminary notes were given as to its absorbability in 65 of 300 cases in which spinograms were made. Observations were carried out at varying intervals following the procedure, with the following results: Roentgenograms of the skull were taken in 48 cases and 14 of these (29 per cent) showed small amounts of pantopaque in the basal cisterns. Little material has appeared dealing with the absorption of pantopaque. Mayfield (1) mentioned that when a few droplets were retained, absorption took place in two to four months. In 2 additional cases in which 3 to 4 c.c. of oil remained, none was present on examination six months later. Ramsey, French, and Strain (3) gave the average estimated absorption rate as 1 c.c. in one year. Wyatt and Spurling (4) obtained follow-up roentgenograms of 6 patients from nine to fifteen months after injection. They found absorption to be more rapid during the first few months in cases with greater oil retention. The higher rate of absorption sometimes observed was believed to be due to the nature of the contrast medium and the emulsifying action of body movement. No pantopaque was observed in films of the skull, cervical or dorsal spine. Our findings agree essentially with those of Wyatt and Spurling except for x-ray studies of the skull. Two hundred and forty-seven follow-up studies have been made at intervals of one to twenty months after injection of pantopaque in a series of 640 myelograms. In the beginning, studies were made of the entire subarachnoid system, including the cervical, dorsal, and lumbosacral spine and skull. Since the cervical and dorsal regions rarely showed evidence of retention, subsequent investigations were limited to the skull and lumbosacral spine. Although many cases show fixation after two to three months, this is not always true, particularly when larger amounts of the medium are retained. This has been demonstrated both fluoroscopically and in successive x-ray studies. No deleterious symptoms or signs have been noted in addition to the findings already recorded (2). Estimates as to absorption were made by first measuring the amount of oil removed at the time of myelography. Successive anteroposterior and lateral films of the lumbosacral spine and skull were then compared to determine the size of the residual pantopaque shadow, which was stated in terms of cubic centimeters. There was a tendency toward a relative decrease in the density, as well as the size, of the residual medium over varying periods of time. All examinations were made by one observer (W.G.P.), to minimize the possibility of error. The following table shows the results, representing an average of the cases studied.