Proteases and especially collagenase injected into the lateral brain ventricles of rats are able to increase the permeability of the blood-brain barrier to trypan blue. Treatment of the rats with anthocyanosides of Vaccinium myrtillis diminishes the permeability increasing effect of collagenase and accelerate the recovery of normal permeability. This effect seems to be related to a less effective enzymatic attack on collagen, as hydroxyproline content in the CSF is increased less after collagenase injection in treated animals than in untreated controls.