The E3 ubiquitin ligase CHIP (C-terminus of Hsc70-interacting protein) is believed to be a central player in the cellular triage decision, as it links the molecular chaperones Hsp70⁄Hsc70 and Hsp90 to the ubiquitin proteaso-mal degradation pathway. To better understand the decision process, we determined the affinity of CHIP for Hsp70 and Hsp90 using isothermal titration calorimetry.