Hexafluorodiethyl ether was administered to 60 of 120 patients randomly selected for convulsive therapy. In the 720 treatments administered to these 60 patients there was no failure in bringing about a grand mal convulsion. Also, there was no evidence of any change in sensitivity or tolerance to the standard convulsive dose with progressive treatment. The convulsive seizure was similar to that produced by electric stimulation, except for a more gradual onset. There appeared to be less immediate postconvulsive anoxia, and immediate postconvulsive psychomotor activity appeared diminished in comparison to ECT. Subjectively, a majority of those patients who had been exposed to both types of treatment felt less apprehensive with the inhalation procedure. From these results it appears that Indoklon is an effective and safe convulsive agent that can be administered safely and conveniently on a large scale basis.