It is well known that the degradation of peptide hormones can contributes to destabilization of normal tissue physiology. Cathepsins have been described as participants in the development of different types of cancer. Considering the pathophysiological enhancement in the activity of proteases such as cathepsins B and their possible colocalization with pancreatic peptide hormones such as insulin, it is conceivable that the pancreatic endocrine function can be affected by an earlier degradation of the mentioned hormone during inflammatory and tumoral processes. The mammalian insulin shows a remarkably high homology between species and the processing of pro-insulin results in the release of biologically active peptide. Insulin acts in the glucose homeostasis, cellular growth/differentiation and energy metabolism. The susceptibility of insulin to cathepsins B activities was verified by using the liquid-chromatography/mass spectrometry system (LC-MS). Cathepsins B was able to hydrolyze the insulin peptide in a few specific points. This hydrolysis was not affected by the presence of heparin. In spite of previous roles attributed to these proteases in pathophysiological events, the obtained results are in agreement with the hypothesis that cathepsins B can participate in degradation of insulin. (Supported by FAPESP, CNPq and FAEP).