The water-rich phase (tissue channels) of the intersititial tissue in rat ileum, knee joint capsules, kidneys, and implanted Guyton's capsules was examined electron microscopically by the SEM of plastic injection models, and by TEM and HVEM of ferrocyanide and ferritin as tracers. It was shown that the channels do in fact exist, and are not just vacuoles. Quantitative estimations of their numbers and diameters were made. These agreed well with estimates made by other methods.