Growth factors, such as transforming growth factor β (TGF-β) and insulin-like growth factors (IGF) I and II, have been shown to exert anabolic effects on bone cells in vitro. Hormones, such as PTH and probably insulin and growth hormone, were recently shown to stimulate bone formation in vivo as well. The aim of the present study was to assess by northern blots, which were quantitated by densitometry, the effects of these anabolic growth factors and hormones in two osteogenic cell populations: CRP 10/30 cells, a clonal cell population derived from primary rat calvarial cells, and IRC 10/30-myc cells, which were established from CRP 10/30 by immortalization. Transcripts for α1(I) collagen, biglycan, osteonectin, osteopontin, and osteocalcin were detected in both cell populations, which is consistent with the phenotype expressed by mature osteoblasts. There were no difference in the basal expression of bone matrix mRNAs between the two cell populations. PTH increased α1(I) collagen mRNA levels in both osteoblastic cells but had no effect on the biglycan transcripts. Neither insulin nor growth hormone affected mRNA levels of either matrix protein after 24 h exposure. All three growth factors, TGF-β, IGF-I, and IGF-II, increased α1(I) collagen transcripts in a time- and dose-dependent manner in both cell populations. Biglycan mRNA levels were enhanced in both osteoblastic lines only by IGF-I and IGF-II, but not TGF-β. The transcriptional effect was ascertained by nuclear run-on assays or actinomycin inhibition. When the effects of TGF-β, IGF-I, and IGF-II on the expression of α1(I) collagen and biglycan mRNAs were compared in the two cell populations, there was a similar pattern of response. The only significant difference between the immortalized cell line and the parent cell population was a stronger stimulation of α1(I) collagen mRNA by TGF-β and a delayed increase in biglycan mRNA levels in IRC 10/30-myc. The results show that the immortalized cell line IRC 10/30-myc is useful to study the modulation of two osteoblastic markers, α1(I) collagen and biglycan mRNA, in response to exogenous factors. Biglycan is little modulated and only by IGFs, whereas PTH, IGF-I and II, and TGF-β strongly increase α1(I) collagen transcripts, confirming their anabolic effects on bone cells in vitro.