Antisera from scleroderma patients that react widely with centrosomes in plants and animals were used to isolate cDNAs encoding a novel centrosomal protein. The nucleotide sequence is consistent with a 7 kb mRNA and contains an open reading frame encoding a protein with a putative large coiled-coil domain flanked by noncoiled ends. Antisera recognize a 220 kd protein and stain centrosomes and acentriolar microtubule-organizing centers, where the protein is localized to the pericentriolar material (hence, the name pericentrin). Anti-pericentrin antibodies disrupt mitotic and meiotic divisions in vivo and block microtubule aster formation in Xenopus extracts, but do not block gamma-tubulin assembly or microtubule nucleation from mature centrosomes. These results suggest that pericentrin is a conserved integral component of the filamentous matrix of the centrosome involved in the initial establishment of organized microtubule arrays.