Barrier between the perineurium of peripheral nerves and the vascular endothelium of endoneurial capillaries. The perineurium acts as a diffusion barrier, but ion permeability at the blood-nerve barrier is still higher than at the blood-brain barrier[GO]. [ http://amigo.geneontology.org/amigo/term/GO:0008065 http://en.wikipedia.org/wiki/Blood-nerve_barrier ]