Centrosomes are the major microtubule nucleating center in the cell; they also contribute to spindle pole organization and play a role in cell cycle progression as well as completing cytokinesis. Here we describe the molecular characterization of a novel human gene, CEP55, located in 10q23.33 that is expressed in multiple tissues and various cancer cell lines. Sequence analysis of the cDNA predicted a protein of 464 amino acids with several putative coiled-coil domains that are responsible for protein-protein interactions. Indeed, we found homodimerization of CEP55 by coimmunoprecipitation. Subcellular localization analysis revealed that endogenous CEP55 as well as an EGFP-CEP55 fusion protein is present at the centrosome throughout mitosis, whereas it also appears at the cleavage furrow in late anaphase and in the midbody in cytokinesis. Neither nocodazole nor taxol interfered with centrosome association of endogenous CEP55, suggesting that it directly interacts with centrosome components rather than with microtubules. In microtubule regrowth assays, overexpression of CEP55 did not enhance or inhibit microtubule nucleation. Together, these data suggest a possible involvement of CEP55 in centrosome-dependent cellular functions, such as centrosome duplication and/or cell cycle progression, or in the regulation of cytokinesis.