PrP(C) is a glycosylphosphatidylinositol (GPI) anchored glycoprotein of unknown function. Misfolding of normal cellular PrP(C) to the pathogenic PrP(Sc) is the hallmark of prion diseases (transmissible spongiform encephalopathies). Prion diseases are characterized by extensive neurodegeneration and early death. Understanding how PrP(C) maintains its correct conformation is a major endeavor of current inquiry. Here we demonstrate a novel interaction between PrP(C) and the J protein family member, Rdj2 (DjA2; Dj3, Dnj3, Cpr3, and Hirip4). The importance of the J protein family in the cellular folding machinery has been recognized for many years. The PrP(C)/Rdj2 association was direct and concentration-dependent. Other J proteins such as CSPalpha and auxilin did not associate with PrP(C) in the absence of ATP, demonstrating the specificity of the PrP(C)/J protein interaction. These findings suggest that the J protein family serves as a 'folding catalyst' for PrP(C) and implicates Rdj2 as a factor in the protection against prion diseases.