A human autoantibody from a schleroderma patient was found to immunostain interphase and mitotic centrosomes in a variety of vertebrate cells. Electron microscopic immunocytochemistry localized this antigen in dense pericentriolar material (PCM) surrounding the centrioles. The meiotic spindle of the mouse egg has no centriole but it exhibited a broad PCM band at each pole. This pattern was also found from the first through fourth mitotic divisions. During this time PCM was found assembled at a single locus in the cell and exclusively in mitotic cells; it was not observable in interphase cells. In the blastocyst, only polar trophoblast cells had characteristic centrosomes throughout the cell cycle. Results suggest PCM can exist, disperse, and reorganize during the cell cycle independently of the centriole, and its distribution in the embryo differs in cells having different fates.