We propose a method for estimating membrane permeability and the intracellular diffusion coefficient using pulsed-gradient spin-echo measurement in combination with numerical simulation. The diffusion signal attenuation of leukocytes was measured with 4pi(2)q(2)(Delta-delta/3) values up to 6000 s/mm(2). For numerical simulations, the cell was modeled as a 15 x 15 microm(2) square with various membrane permeabilities and intracellular diffusion coefficients. Minimization of the difference in signal attenuations between the measurement and the simulation enabled estimations of these unknown parameters for the leukocytes. A cell sample of 2.17 x 10(8) cells/mL had a membrane permeability and an intracellular diffusion coefficient of 23 mum/s and 8.9 x 10(-4) mm(2)/s, respectively.