dynamics of crosslinked poly (N-isopropylacrylamide) gel have been studied by means of pulsed-gradient spin-echo (PGSE) H-1 nuclear magnetic resonance (n.m.r.), pulse H-1 n.m.r. and H-1 n.m.r. imaging. The selfdiffusion coefficients of HDO (D-HDO) in D2O (containing a small amount of HDO) in the gels with various degree of swellings were determined by the PGSE H-1 n.m.r. method. From these experimental results, it was found that the D-HDO is decreased as the degree of swelling is decreased, and D-HDO in the gels with a constant degree of swelling in going from 20 to 45 degrees C is transitionally decreased at about 32 degrees C, which corresponds to the phase transition temperature. From the detailed analysis of proton spin-spin relaxation time T-2 determined by the pulse H-1 n.m.r. method, the process of the volume phase transition of the gel has been elucidated. Furthermore, spatial information about the molecular motion of water in the gel sample was obtained by T-2 enhanced H-1 n.m.r. imaging.