The hypothalamus and myocardium of 54 patients (27 males and 27 females, age range 12 to 73 years) who died after subarachnoid hemorrhage (SAH) were examined histologically. In 42 patients, hypothalamic and myocardial lesions were found; in seven, hypothalamic lesions only; and in five, no hypothalamic nor myocardial lesions. A similar examination was performed on a control group of 25 patients (12 males and 13 females, age range 17 to 70 years) who had died from a variety of causes, all producing raised intracranial pressure. In these, no lesions were found in either the hypothalamus or the myocardium. The age of the patient, the site of the vascular pathology, and whether an operation was performed appeared to have no effect on the occurrence of hypothalamic and heart lesions; however, there was a correlation between these lesions, progressive neurological deterioration, and varying pulse rates and blood pressures. This study produces further evidence of the involvement of the autonomic nervous system in some of the deleterious effects of SAH, and a suggestion is made as to possible treatment.