The presence of a degradation product of alprazolam tablets that emerged throughout a short-stability assay has been determined and properly characterized. For this purpose an efficient methodology has been successfully applied, including SPE and HPLC methods for isolation and purification, respectively. LC/MS, MS/MS, 1H NMR, 13C NMR, UV and IR have been employed for structural elucidation confirming the identity of this impurity as 7-chloro-1-methyl-5-phenyl-[1,2,4]triazolo[4,3-a]quinolin-4-amine or triazolaminoquinoleine. The impurity, previously described as a long-term photodegradation product of alprazolam active pharmaceutical ingredient, was rapidly formed in the absence of light, but required the presence of excipients and its rate of formation increased with heat and humidity. In addition, a LC method has been developed and validated including triazolaminoquinoleine for the adequate determination of alprazolam and its mayor degradation product in tablets as pharmaceutical forms.