The diffusion rate of the enzyme ribonuclease into a porous chromatography support material was measured at 298 K. An effective diffusion coefficient of 5.0 × 10^–7 cm²/s was obtained from an experiment based on diffusion of the enzyme through a single cylindrical pore. Estimate the pore diameter (dpore) needed to achieve this effective diffusion coefficient. The molecular diffusion coefficient of ribonuclease in water is 1.19 × 10^–6 cm²/s at 298 K, and the diameter of this molecule is 3.6 nm.