In a study of 120 patients with chronic multiple sclerosis the effects of treatment with 100% oxygen at 2 atmospheres absolute for 90 min daily for a total of 20 exposures were compared with those of normal air at normal pressure for a similar length of time within the same compression chamber. No patient in either group showed any improvement on the Kurtzke disability status scale. 12 of 51 patients in the hyperbaric-oxygen group and 3 of 47 control patients improved on the Kurtzke functional systems scale on the subjective bowel/bladder parameter only. Such a degree of improvement can also be achieved with medication for urinary symptoms, but none of the patients in this study received such medication. The short-term results of this trial do not support the claims made for hyperbaric oxygen in the management of multiple sclerosis.