OBJECTIVE: The pathophysiology of delayed cerebral ischemia (DCI) following aneurysmal subarachnoid hemorrhage (aSAH) has not been fully evaluated. The aim of this study was to evaluate the dynamics of lactate and lactate dehydrogenase (LDH) in carotid cisternal cerebrospinal fluid (CSF), and to discuss their effectiveness as markers of early brain injury (EBI) and DCI following aSAH. PATIENTS AND METHODS: Among 91 consecutive aSAH patients treated between January 2012 and March 2019 at National Hospital Organization Beppu Medical Center, 19 patients (20.9%) were eligible for this retrospective study. Concentrations of lactate and LDH in carotid cisternal CSF within 14 days after onset of aSAH were evaluated. RESULTS: Six of the 19 patients (31.6%) had a history of DCI. Both lactate and LDH levels in carotid cisternal CSF were significantly higher in the DCI group than in the non-DCI group on postbleeding day (PBD) 1-2, 3-4, and 5-6. Interestingly, neither lactate nor LDH levels in blood differed significantly between DCI and non-DCI groups on PBD 1-2. CONCLUSIONS: Lactate and LDH concentrations in carotid cisternal CSF may vividly reflect the EBI and may thus represent predictive biomarkers of DCI following aSAH.