We reported previously that C-type natriuretic peptide (CNP) promotes the differentiation and mineralization of osteoblastic cells [Am. J. Physiol. 270 (Cell Physiol. 39): C1311-C1318, 1996]. However, little information is available about the mechanism of action of CNP in differentiating osteoblastic cells. Using the technique known as differential display-polymerase chain reaction, we attempted to identify the mRNAs whose levels are regulated by CNP in mouse clonal preosteoblastic MC3T3-E1 cells. One species of mRNA whose level was increased by CNP was 99% homologous to the 3'-untranslated region of a mouse gene for biglycan (BGN), a small proteoglycan. BGN is known to be involved in bone formation by osteoblastic cells. Therefore, we investigated the relationship, during the formation of mineralized nodules, between CNP and BGN using calvarial osteoblast-like cells (ROB cells) from newborn rats, that are a good model for studies on bone formation in vitro. Northern blot analysis revealed that transcription of the mRNA for BGN was up-regulated by CNP in ROB cells on days 6 and 8, whereas no effect of CNP was observed on days 3 and 12. Brief treatment with 10(-7) M CNP on days 3 through 9 exclusively enhanced the deposition of calcium, a result that suggests that CNP might regulate the expression of mineralization-related genes and, probably, the gene for BGN during a specific time period.