In order to explore the applicability of daily cerebral autoregulation monitoring through routine utilization of the transient hyperaemic response (THR) test in patients after aneurysmal subarachnoid haemorrhage (SAH), we performed THR tests daily in 50 consecutive patients with verified SAH. Out of 1167 studies, the test results were acceptable during 954 procedures (81.5%). 310 negative (32.5%; range 0.75-1.099; mean 1.03) and 644 positive (67.5%; range 1.10-1.77; mean 1.19) test results were obtained. Multiple logistic regression analysis revealed that the registration of negative THR in a middle cerebral artery (MCA) during the period of critical care was related to the patients' poor clinical grade (p-0.02) and Fisher CT-grade (p-0.04) on admission, to the development of vasospasm (p-0.003) and to the detection of ipsilateral intracerebral haemorrhage and/or cerebral infarction (p-0.01). The frequent registration of negative THR tests (negative results in > 30% of all the tests in an MCA) was independently related to the detection of ipsilateral intracerebral haemorrhage and/or cerebral infarction (p-0.0001). THR tests provide information about intracranial alterations and can be safely performed as a routine monitoring tool after SAH.