Miscibility of 17beta-estradiol and Eudragit RS in solid dispersions was determined by modulated temperature differential scanning calorimetry (MTDSC). A reduction of the 17beta-estradiol melting point in Eudragit RS solid dispersions was observed by MTDSC using heating program I in which the maximum temperature in the first heating run was lower than the 17beta-estradiol melting point. The melting point depression of 17beta-estradiol in solid dispersions as a function of composition could be explained by the Nishi-Wang equation indicating an interaction between 17beta-estradiol and Eudragit RS in the system. A variation of glass transition temperature (T(g)) of 17beta-estradiol in Eudragit RS solid dispersion was observed by MTDSC using heating program II in which the maximum temperature in the first heating run reached the 17beta-estradiol melting point. In the second heating run of heating program II, 17beta-estradiol was in an amorphous form blended with Eudragit RS. The variation in T(g) of amorphous 17beta-estradiol blended with Eudragit RS could be explained by the Kwei equation, a modified version of the Gordon-Taylor equation. The parameter estimates from the Kwei equation were consistent with an interaction between 17beta-estradiol and Eudragit RS, which was due to inter-associated hydrogen bonding as deduced from the FTIR spectra of the blends.