Hyperbaric oxygen therapy was utilized in a case of fulminant mucormycosis of the maxilla, orbit and temporal bone. The patient had refused radical surgery and death seemed iminent in spite of aggressive medical management of diabetic ketoacidosis, amphotericin B and wide surgical drainage of the maxillary and ethmoid sinuses with orbital decompression. Hyperbaric oxygen was instituted on the following theoretical premises: 1. It would provide oxygenation of tissues distal to occluded arteries, thereby increasing local survival and decreasing acidosis, 2. resultant lessening of acidosis would slow or inhibit rapid growth of the organism, and 3. oxygen in sufficient concentration is fungicidal. The rapid progress of the mucormycosis was arrested. Cultures of tissue prior to hyperbaric oxygen treatment produced heavy growth of Rhizopus, and tissues cultured after therapy grew only bacterial contaminants. The patient survived for 3 mo. only to succumb to Pseudomonas meningitis secondary to necrotic bone and epidural abscess of the middle cranial fossa. Rhinocerebral mucormycosis is a fulminant and frequently fatal disease. No survivors were reported before extensive surgical debridement was utilized. Survival improved to 50% with the addition of amphotericin B. Early diagnosis and correction of underlying acidosis has further improved this to 85%. The response to hyperbaric oxygen in this case report possibly introduces a promising new adjunct to therapy of this serious disease.