Recrystallization is one of the main problems concerning the stability of solid dispersions. Different analytical methods were applied showing that no recrystallization occurred after treating melt extruded solid dispersions with 17 beta-Estradiol as the model drug with heat or water vapor. A skillful choice of excipients--a combination of polymers and additives--could be the reason for improving the stability. The requirements of the USP 23 for Estradiol tablets of 75% dissolved drug after 60 min were fulfilled after storing the tablets for 6 months at 40 degrees C/75% RH. By observing the change in glass transition temperature, DSC analysis showed that the solid dispersions were stable against thermal stress. Isothermal microcalorimetry as well as moisture absorption gravimetry were methods to prove the stability of the solid dispersions against water vapor.