Pore-size distributions have been measured for cationic acrylamide-based hydrogels of different compositions maintained at the same swelling capacity (27.8 ± 0.7 g swollen gel/g dry gel) by varying the ionic strength of the surrounding solution. Swelling equilibria were measured at about 6°C in pure water and aqueous sodium azide solutions ranging in concentration from to 10−3to 10−1M. The mixed-solute-exclusion method (introduced by Kuga) was used to obtain the experimental solute-exclusion curve, which represents the amount of imbibed liquid inside the gel inaccessible to a solute of radiusr.The pore-size distribution was obtained by using Casassa's Brownian-motion model and numerically solving the Fredholm integral equation. The modes of the pore radii range from 20.4 to 47.1 Å for acrylamide-based hydrogels containing varying amounts of cationic comonomer (1.5 and 4.0 %M), crosslinker (0.3 and 1.0 %C), and initial concentration of total monomer (15 and 35 %T).