Pericentrin was first identified as a mouse centrosomal protein and is now referred to as pericentrin A. A larger homologous protein in humans with a C-terminal calmodulin-binding domain was later identified as pericentrin B. Pericentrin has been shown to be one of the key components in ciliogenesis, but in vivo pericentrin products have remained ambiguous. Here we characterized pericentrin isoforms in mice. Two pericentrin transcripts of 9.5 and 6.9 kb were recognized on the mouse tissue Northern blots, while a cRNA probe for a 5'-terminal sequence shared by pericentrin A and B failed to hybridize to the 6.9-kb message. Two pericentrin cDNAs were identified, which encoded pericentrin B and a novel isoform, pericentrin S, sharing with pericentrin B a C-terminal calmodulin-binding motif. Three pericentrin proteins of 360, 255, and 250 kDa revealed by immunoprecipitation analysis were thought to correspond to pericentrin B, pericentrin S, and an unknown N-terminal product.