The mass transfer characteristics of cellulosic membranes nearly devoid of any charge or adsorption property were investigated in vitro for the design of hemodialyzer. Overall membrane resistance（O.M.R.） of cellophane produced by Union Cellophane(Seoul, Korea) was determined by a dual closed-loop dialysis technique with which the effects of blood flow rate, dialyzate flow rate and molecular size on O. M. R. were examined. Ultrafiltration experiment was performed by making use of Amicon ultrafilter with which solute rejection was determined covering M. W. 60 to 44,000. Solute radius(Stokes-Einstein radius) is found to be more reasonable parameter in estimating membrane resistance than molecular weight. The correlations for cellulosic membranes have the following formula.
For membrane 1（22μ thickness, Union Cellophane, Seoul, Korea）
log（R₀）=2.224 log(r₀)+0.745
For membrane 2（38μ thickness）
log（R₀）=1.326 log(r₀)+0.945
where R₀ : overall membrane resistance（min/cm）
r₀ : Stokes-Einstein radius,（Å）.
The kinetics of metabolic wastes（urea, creatinine） of the uremic patient treated by hemodialyzer made of membrane 2(37μm dry thickness, Union Cellophane, Seoul, Korea) was simulated with computer using a two compartment model.