The nonisothermal behavior of amorphous alpha,alpha-trehalose has been studied in order to identify the factors influencing the recrystallization process. Particular emphasis has been placed on examining the effect of differential scanning calorimetry (DSC) pan type and initial water content on the thermal response. Samples of freeze-dried trehalose with water levels up to 6% w/w were sealed in pinholed and hermetically sealed pans and analyzed using DSC at a scanning rate of 10 degreesC/min in conjunction with thermogravimetric analysis (TGA), with the dihydrate studied in pinholed pans for comparison. The dihydrate was found to exhibit two endotherms at ca. 100 degreesC and 122 degreesC, followed by a further endotherm at 211 degreesC that was attributed to melting of the anhydrate. Isolation of the material following the first endotherm indicated that the material generated at this temperature was the T-gamma form. Amorphous material heated in pinholed pans exhibited an exotherm at ca. 100-150 degreesC (the value depending on water content) when the initial water levels were 4.1% or below. This response was accompanied by dehydration and was attributed to the formation of the crystalline anhydrate. Higher water content samples, however, showed an exotherm followed immediately by an endotherm, with the water loss taking place in two distinct stages. XRD studies indicated that these samples initially crystallized into the T-gamma form, followed by subsequent dehydration to the anhydrate. Samples analyzed in hermetically sealed pans showed a single exotherm between 100 and 150 degreesC followed by a broad endotherm between 150 and 200 degreesC, with higher water content samples having lower values for both events. XRD indicated that the exotherm and endotherm corresponded to the formation and fusion of the T-gamma form, respectively. The study has therefore shown that the recrystallization behavior of amorphous trehalose is dependent on both the initial water content and the environment in which recrystallization takes place.