The kinetics of one-dimensional gel swelling and collapse for large volume changes were described by a Fickian model which accounts for the movement of the gel surface. For a constant mutual diffusion coefficient, D-m, the fractional approach to equilibrium, F, is a function only of dimensionless time, tau(0), and the equilibrium volume ratio, Phi. Gel collapse is faster than swelling when D-m is the same for both. Swelling curves, the variation of F with root tau(0), were computed for planar, cylindrical and spherical geometries with constant D-m. For slabs the swelling curves are initially linear for all Phi values, while for cylinders and spheres the swelling curves are linear for small Phi values, but sigmoidal for Phi greater than or equal to 2.5. For 0.5 less than or equal to Phi less than or equal to 2, a simple method gives experimental values of D-m which account for the movement of the gel boundary. Experimental data for weakly ionic poly(N-isopropylacrylamide) gel spheres in water (Phi = 15) and for non-ionic poly(N-isopropylacrylamide) gel disks in water (Phi = 7.7) were well fitted by the model.