Molecular chaperones prevent irreversible protein aggregation and misfolding. Protein aggregation and misfolding are processes usually associated with the so-called conformational diseases, like Alzheimer and Parkinson diseases. To date, a large number of proteins have been identified as components of amyloid fibrils in human amyloidoses. However, no chaperones or associated co-chaperones have yet been identified as amyloidogenics. Here we present results with human Hsp40A, a co-chaperone of an important chaperone system, the Hsp70, which binds nascent polypeptides helping their folding. This protein has been cloned, purified, and had its structure characterized at low resolution (Borges, J.C., Hannes, F., Craievich, A.F., Ramos, C.H.I. (2005). J. Biol. Chem. 280, 13671-13681). Recently, we identified that this chaperone, a protein with major alpha-helical secondary structure, thermally unfolded through a beta-sheet rich intermediate which stained with the amyloid-specific dye Thioflavin-T. An MTT (3-(4,5-dimethylthiazol-2-y1)-2,5-diphenyltetrazolium bromide) assay showed that an aggregated amyloid-like form of Hsp40A was citotoxic for mammal's cells. Therefore, to our knowledge, these are the first experiments to show that a protein belonging to the human chaperone family has amyloidogenic characteristics. The relevance of these results is of great importance and will be discussed.