c-AMP, c-GMP, HVA and 5 HIAA cerebrospinal fluid levels were investigated in 18 patients with subarachnoid haemorrhage (SAH). The main findings in the acute stage after SAH were represented by a marked increase of c-AMP and 5 HIAA values, whereas HVA levels were only slightly higher. In the chronic phase c-GMP levels turned out to be significantly increased, and were clearly related to intracranial hypertension. 5 HIAA and particularly HVA levels were decreased, probably due to the functional and anatomical lesion of the periventricular adrenergic structures, following the raised intracranial pressure.