The 6-kDa early secretory antigenic target (ESAT-6) and culture filtrate protein-10 (CFP-10), expressed from the region of deletion-1 (RD1) of Mycobacterium tuberculosisH37Rv, are known to play a key role in viru-lence. In this study, we explored the thermodynamic and biochemical chan-ges associated with the formation of the 1 : 1 heterodimeric complex between ESAT-6 and CFP-10.