Differential scanning calorimetry (DSC) combined with a curve-fitting program was utilized to quantitatively determine the polymorphic composition of famotidine in the compacts prepared by different compression treatments. Two types of famotidine compacts (compact I or II) were prepared by compressing a conical shape or a flattened shape of powder bed of famotidine form B. The compact I was constructed by a transparent region in the center with an opaque region surrounded outside, but the compact II was formed by a whole opaque region only. A drilled disc sample was prepared and then directly determined by DSC analysis. The Raman spectral results clearly indicate that all the compacts whether in any region before DSC determination were only of famotidine form B and independent of compression pressure applied. Under DSC determination, however, the curve-fitted relative compositions of form B in the drilled disc I sample were gradually reduced to 23-24% with the increase of compression pressure, whereas the curve-fitted relative composition of form A was slowly increased up to 76-77%. A transitional phase of famotidine form B (form B*) in the transparent region of the compact I after applying >150 kg/cm(2) of compression pressure was easily detected, and then transformed to famotidine form A under DSC heating process. But this transitional phase and polymorphic transformation of famotidine could not be detected by other spectroscopic methods. This suggests that the DSC heating system was a preferred method not only to quantitatively analyze the polymorphic transformation of famotidine but also to find a newly transitional phase of famotidine in the compressed compact.