Abstract: Up to now,the studies on the centromere proteins are almost carried out in yeast and higher organisms in the world.In this paper we report our studies on centromere proteins in one kind of ciliates,which is much lower than yeast in the evolutionary position mainly with indirect immunofluorescent microscopy and western immunoblotting techniques using two ACA sera,ra-ACA-2,Maca-2,and mAb37A5 as probes.The control material in the study is human HepⅡ cell.With immunofluorescent stain with Chinese ACA antiserum,in the interphase nucleus of HepⅡ cells only very minute pots-precentromere could be observed.This means that the ACA antiserum can actually and specifically recognize the protein components of centromer/kinetochore.When Tetrahymena,was stained with the same technique,there were only patched within nuclei composed of minute fluorescent spots;no precentromere could be distinguished,although all the nuclei gave positive reaction.After immunobloted with Chinese ACA serum and SH serum,the positive band-pattern (from 14 Kd to 140 Kd) of Tetrahymena was highly similar to the band-pattern of human HepⅡ cells.The blotting results with Maca-2 antibody showed that HepⅡ cells gave two bands (80 Kd,stained deely and 120 Kd,stained slightly),Tetrahymena,gave three positive bands (80 Kd,120 Kd,and 150 Kd).The blotting results with ra-ACA-2 antiserum showed that Hep Ⅱ and Tetrahymena all gave 50 Kd,60 Kd and 80 Kd bands.In the immunoblotting with monoclonal antibody mAb37A5,HepⅡ cells gave two bands very similar to those of CHO cells.Tetrahymena gave only one band with molecular weight somewhat lower than 140 Kd.The results described above indicat the high similarity in the centromere/kinetochore protein components between HepⅡ cells and the Tetrahymena.must have emerged earlier in life evolutionary history.