Effects of cerebrospinal fluid (CSF) pressure elevation in six dogs with ganglionic and alpha adrenergic blockade were compared to a previously studied group of dogs with only alpha adrenergic blockade. There were no significant hemodynamic differences. Decreased peripheral vascular resistance and increased cardiac output during elevated CSF pressure and alpha adrenergic blockade were probably due to circulating beta adrenergic agonists. No differences were found in plasma norepinephrine and epinephrine levels from the control period to the cerebral hyperemia period ten minutes after the CSF pressure was returned to normal. Cerebrospinal fluid pressure was elevated in 100 mm Hg increments to 400 mm Hg in eight dogs. Pulmonary arterial and left atrial pressures were maximal during the 200 and 300 mm Hg CSF pressure periods. Plasma norepinephrine levels did not change from the control period to the 300 mm Hg CSF pressure period.