Peptidergic fibres innervating human embryonic and adult cerebral blood vessels were screened for calcitonine gene-related peptide, neuropeptide-Y and substance-P immunopositive fibres, the mediaadventitia border displayed a network-like fibre arrange ment. There was no significant difference either in the distribution of the individual peptidergic fibres or in the age-dependent appearance of peptidergic networks. On the basis of these results it seems to be unlikely that the different clinical course of juvenile and adult subarachnoid haemorrhages could be the result of an age specific difference of peptidergic fibre distribution influencing the neurogenic mecha nisms of cerebral autoregulation.]