The ionic transfer number in an electrolyte solution in the pores of a narrow pored collodion membrane depends much more on the concentration than it does in a free aqueous solution. The potential difference of two solutions of the same electrolyte in different concentration depends largely on the concentration range. The ratio of the concentrations on the two sides was always 1:2 in the experiments; the concentration range was varied. It is shown that the transfer number of Cl, calculated from the P.D. measured, is very small in dilute solution (down to .02 and less in some cases), whereas it approaches the value .5 holding for free aqueous solutions when the concentration range is raised. The differences for the transfer number of Cl, according to the cation (H, K, Na, Li), can be recognized and show the same order as in free aqueous solution. But even in LiCl, where in an ordinary aqueous solution the transfer number of Cl is always > .5, this number is very low in the case of the membrane (e.g. < .05 in .01 M solution).