There are few reports concerning the sortingmechanisms of mammalian HSP60 into the mitochondria from the cyto-plasm. In the present study we investigated the protein import system. Based on immunoblotting and immuno-histochemistry, HSP60 was detected in both the cytoplasm andmitochondria. The purified cytoplasmicHSP60 showed chaperone activity, and the protein was imported into the mitochondriain vitro by a mitochondrial import assay.