Hydrogels with varying cross-linking ratio and ionic content were prepared from interpenetrating networks of poly(vinyl alcohol) and poly(acrylic acid). Equilibrium swelling studies were conducted and the average molecular weight between cross-links, (M) over bar(c), and mesh size were determined. Hydrogels with large (M) over bar(c) values were found to swell to a greater extent than those with small (M) over bar(c) values. It was also observed that an increase in (M) over bar(c) yielded faster swelling and deswelling rates, as the rates for membranes with (M) over bar(c) = 18,000 were about twice as fast as were the rates for membranes with (M) over bar(c) = 34,000. Oscillatory swelling behavior was investigated in response to changes in the pH and ionic strength of the swelling medium. A change in pH from 3 to 6 caused an ionization of the hydrogels and an increase in the weight swelling ratio, with a greater increase exhibited by IPNs with a higher ionic content. Increase in pH also caused an increase in the average mesh size.