Hsp40 is a co-chaperone of Hsp70 that correctly folds polypeptides that exist in non-native forms. The C-terminal peptide-binding domain (CTD) of the human Hsp40 Hdj1 has been purified and crystallized. In the presence of the C-terminal octapeptide of human Hsp70, four types of crystals, types I-B, II, III and IV, were grown and diffracted to 1.85, 2.51, 2.10 and 2.80 Å resolution, respectively. In the absence of the octapeptide, type I-A crystals of the CTD were grown that diffracted to 2.05 Å resolution. The full-length Hdj1 was also purified and crystallized (type V crystals); the crystal diffracted to 3.90 Å resolution.