We report a method using Trypan blue staining to detect primo-vessels in the nervous system on internal organs or in the skin of rat. We applied this technique to visualize the primo-vessels and primo-nodes in the brain, spinal cord and sciatic nerve of a rat. Primo-vessels and primo-nodes were preferentially stained at nerves, blood vessels, or fascia-like membranes and turned blue after the spread and washing of Trypan blue. The physiological role of the primo-vessels within the nervous system is an important question warranting further investigation.