Detecting and analysing of the amorphous phase are increasingly important in pharmaceutical technology. The amorphous or glassy state has a several advantages and disadvantages. The amorphous form can be applied in deliberate amorphization, when active pharmaceutical ingredient (API) is formulated in glassy state, or this form can appear accidentally during formulation or storage. The aim of this study was to characterize glass-forming properties of 13 different materials. Differential Scanning Calorimetry (DSC) was used as an analytical technique and T(g) and T(m) values were determined. The equation of T(g)/T(m) (K/K) was applied to determine the glass-forming tendencies. We made 2 groups of investigated substances. The first group was that we could not amorphized: tenoxicam, mannitol, niflumic acid, theophyllin and lidocain. The second group contains materials, which could be prepared in glassy form. This group can be divided into 2 sub-groups: poor-glass formers and good-glass formers. Poor-glass formers are following: meloxicam, ibuprofen and piroxicam. Good-glass formers are lacidipine, gemfibrosil, sorbitol, loratadine, chlorhexidine and clopidogrel hydrogensulfate.