Human and rat osteoblast-like cells express stathmin, a growth-regulatory protein. We used the differential display polymerase chain reaction method of Liang and Pardee (Science (1992) 257:967-971) to identify a growth-regulatory protein, stathmin or oncoprotein 18, in human and rat osteoblast-like cells. When messenger ribonuleic acid from human osteosarcoma (Saos-2) cells treated with 10(-8)M 1,25-dihydroxyvitamin D3 was compared with that of cells treated with vehicle alone by this method, we observed an increase in the intensity of a band that on subsequent DNA sequence analysis was found to encode stathmin. We examined normal human osteoblast-like cells, transformed human osteoblast-like cells (HOBIT), human osteosarcoma cells (Saos-2), and rat osteoblast cell (ROS 17/2.8, ROS 25/1) lines for the presence of the messenger RNA for stathmin. All osteoblast-like cells examined expressed the RNA for this protein. Western analysis of the protein of these cells with a polyclonal antibody directed against stathmin showed the presence of a M(r) 19,000 band. We conclude that human and rat osteoblast-like cells express stathmin and that this protein could play a role in regulation of the growth of these cells in response to various hormonal stimuli.