Abstract: When typical dinoflagellate,Crypthecodinium cohnii,was detected with immuno-fluorescent microscopy,its nucleus gave positive reaction to ACA serum against human centromere/kinetochore proteins.However,in its nucleus,just as in nuclei of Tetrahymena and Euglena,spot-like precentromeres have never been found.The immuno-blotting detections with the monoclonal antibody,mACA-2,against human centromere protein,CENP-B,showed that Crypthecodinium and the special dinoflagellate,Oxyrrhis marina,gave the same result which was correspondent with those given by Tetrahymena,Euglena and human Hep-2 cells.With the CENP-B polyclonal antibody,ra-ACA-2,the two dinoflagellates,other protists and Hep-2 cells also gave the results identical to each.These results indicated that CENP-B was highly conservative in eukaryotic evolution.In fact,all the centromere/kinetochore proteins are quite conservative.Therefore,in the immuno-blotting detections done with ACA serum,the positive bands of Tetrahymena and Euglena are quite similar to those of human Hep-2 cells.The bands of the special dinoflagellate,Oxyrrhis,are similar to other protists.although a few bands are absent.However,the bands of typical dinoflagellate are obviously different from Oxyrrhis Sand other eukaryotes.It means that two dinoflagellates are far from each other.The results obtained with the monoclonal antibody,mAb37A5,against the kinetochore proteins of CHO cells,also proposed the above suggestion.In the detections,Tetrahymena gave only a 120 kD band; Euglena and Oxyrrhis gave two bands (45 kD and 120 kD),while Crypthecodinium and archezoan,Giardia,gave three bands (45 kD,50 kD and 120 kD).It is very interesting that various archaebacteria all gave the 45 kD band and the 50 kD band (the third band is of 40 kD)(Wu et al.,1996b).