[en] This study aimed to develop a drug delivery system of superior drug releasing properties and to find factors to control the properties of microspheric and hydrogel polymers. Further, techniques to control the drug release properties by γ-ray exposure were investigated. The effects of gelatin concentration and the degree of cross linkage on the release rate of temperature-responding hydrogel were investigated in the previous year. In this year, the mobility of a hydrogel polymer was investigated using dynamic light scattering photometry. Biodegradable polymer such as dextran, gelatin, polyhydroxyethylaspartamide was dissolved in dimethylaminopyridine and incubated with glycidylymethacrylamide to produce its methacryl derivatives and the polymer solution was exposed to γ-ray in the presence of a drug. Then, ¹H-NMR spin-spin relaxation time was determined for estimation of mobility and mesh size of the polymer. In addition, the drug release rate for the hydrogel polymer after γ-ray exposure was estimated. The drug release rate of hydrogel was demonstrated to be dependent on its mesh size and the mobility of the polymer was closely correlated to the mesh size. Thus it was demonstrated that spin-spin relaxation time (T₂) was available as an indicator for mobility of gel-like polymers. Up to now, synthetic polymers that were not biodegradable have been used as stimuli-responding gel. However, it became possible to produce a stimuli-responding gel by the hydrogel preparation method using γ-ray irradiation. (M.N.)