Stathmin is a ubiquitous phosphoprotein proposed to play a general role as an intracellular relay integrating diverse regulatory signals of the cell's environment. We used a rat stathmin probe to isolate two classes of cDNAs coding for the human protein and corresponding to the usage of different polyadenylation sites. Compared to the rat sequences, they displayed a very high conservation both at the nucleic acid and the deduced protein sequence levels, with a single conservative amino acid difference. Further analysis of the protein sequence revealed novel putative phosphorylation sites, as well as internal repeated sequences which might reflect structural features involved in the molecular mechanisms by which stathmin fulfills its biological functions. The extreme conservation of the entire stathmin sequence further stresses the essential and general role of stathmin in cell regulations.