The authors studied the behavior of vessels penetring the nervous paren-quima in the basal paraolfatory space after an intravenous injection of the hipertonic sodium chroriae solution (20/1000), plus a 1% India ink solution injected via subarocnoidal space. The experiments were performed in 10 dogs of different races keeping 6 as controls. The experiment followed Mallory's method and consisted in cutting series of 20 microns sections, going from tne surrace down to 10mm deep, 10 plates (in eacn case; of the vessels and the pio-glial membrane were drawn up with tne aid of a "'camera lucida". The statistical analysis showed a significant enhance in the perivascular space due to the hipertonic solution which seems to results from an osmotic phenomenon through the pio-glial membrane. In this way, the pio-glial membrane can be considered as an active structure in the neuronal-ghal-meninge complex.