The monoclonal antibody CTR210 raised against isolated human centrosomes strongly decorates the centrosome and more weakly a domain congruent with the Golgi apparatus in several animal cells (HeLa, 3T3, CHO, PtK2). Both decorations resist Triton extraction in conditions which totally extract the Golgi apparatus, as judged by galactosyltransferase decoration. A 67 kDa centrosomal antigen can be demonstrated in human cells with this antibody. CTR210 also decorates the centrosome or associated structures in several systems, including unicellular eukaryotes such as dinoflagellates or ciliates. A 72 kDa antigen has been identified and purified from the dinoflagellate C. cohnii and its NH2-terminal sequence partially established. It shows a close homology with HSP70 proteins. The possibility that the 72 kDa antigen belongs to this chaperone family was further supported using a mAb reacting, in most species, with HSP70. A polyclonal antibody raised against the 72 kDa antigen from C. cohnii decorates the centrosome in human cells and reacts with the CTR210 centrosomal 67 kDa antigen. These results suggest that specific chaperone proteins are associated with the centrosome in eukaryotic cells. The centrosomal chaperones could participate in the microtubule nucleation reaction or in the process of centrosome assembly.