The equivalent pore radius of a semifinished upper leather was studied. The technic employed was based on a very well known method used by the membrane biophysic research workers. It consists in the measurement of hidrodynamic and diffussion fluxes (at zero concentration and pressure difference, respectively)betveen two chambers separated by the leather sample« The equivalent pore radius was calculated from the results obtained for both fluxes, and it is of the order of one micron.