A 52-year-old man experienced progressive tonic-clonic activity soon after undergoing a myelogram accompanied by an intrathecal injection of Omnipaque. The activity progressed to seizures, hyperthermia, and acidosis. He was intubated, cooled, and treated symptomatically. His creatinine kinase rose to 60,000 IU/L. He eventually recovered completely. This distinct set of clinical signs renders the syndrome easily recognizable. Although this syndrome superficially resembles malignant hyperthermia, the pathophysiology is different. Survival depends on prompt recognition and rapid symptomatic treatment. Treatment with dantrolene sodium is not necessary.